Pub Date : 2022-06-27eCollection Date: 2022-05-01DOI: 10.1063/4.0000146
Lorenzo Restaino, Deependra Jadoun, Markus Kowalewski
Linear off-resonant x-ray Raman techniques are capable of detecting the ultrafast electronic coherences generated when a photoexcited wave packet passes through a conical intersection. A hybrid femtosecond or attosecond probe pulse is employed to excite the system and stimulate the emission of the signal photon, where both fields are components of a hybrid pulse scheme. In this paper, we investigate how attosecond pulse trains, as provided by high-harmonic generation processes, perform as probe pulses in the framework of this spectroscopic technique, instead of single Gaussian pulses. We explore different combination schemes for the probe pulse as well as the impact of parameters of the pulse trains on the signals. Furthermore, we show how Raman selection rules and symmetry consideration affect the spectroscopic signal, and we discuss the importance of vibrational contributions to the overall signal. We use two different model systems, representing molecules of different symmetries, and quantum dynamics simulations to study the difference in the spectra. The results suggest that such pulse trains are well suited to capture the key features associated with the electronic coherence.
{"title":"Probing nonadiabatic dynamics with attosecond pulse trains and soft x-ray Raman spectroscopy.","authors":"Lorenzo Restaino, Deependra Jadoun, Markus Kowalewski","doi":"10.1063/4.0000146","DOIUrl":"https://doi.org/10.1063/4.0000146","url":null,"abstract":"<p><p>Linear off-resonant x-ray Raman techniques are capable of detecting the ultrafast electronic coherences generated when a photoexcited wave packet passes through a conical intersection. A hybrid femtosecond or attosecond probe pulse is employed to excite the system and stimulate the emission of the signal photon, where both fields are components of a hybrid pulse scheme. In this paper, we investigate how attosecond pulse trains, as provided by high-harmonic generation processes, perform as probe pulses in the framework of this spectroscopic technique, instead of single Gaussian pulses. We explore different combination schemes for the probe pulse as well as the impact of parameters of the pulse trains on the signals. Furthermore, we show how Raman selection rules and symmetry consideration affect the spectroscopic signal, and we discuss the importance of vibrational contributions to the overall signal. We use two different model systems, representing molecules of different symmetries, and quantum dynamics simulations to study the difference in the spectra. The results suggest that such pulse trains are well suited to capture the key features associated with the electronic coherence.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2022-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9239728/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"40552734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Bach, A. Feist, M. Möller, C. Ropers, S. Schäfer
Optically excited nanostructures provide a versatile platform for the generation of confined nanophononic fields with potential (non-)linear interactions between different degrees of freedom. Control of resonance frequencies and the selective excitation of acoustic modes still remains challenging due to the interplay of nanoscale geometries and interfacial coupling mechanisms. Here, we demonstrate that a semiconductor membrane patterned with a platinum stripe acts as a tailored source for high-frequency strain waves generating a multi-modal distortion wave propagating through the membrane. To locally monitor the ultrafast structural dynamics at a specific distance from the deposited metal stripe, we employ ultrafast convergent beam electron diffraction in a laser-pump/electron-probe scheme. Experimentally observed acoustic deformations are reproduced by numerical simulations in a continuous medium model, revealing a spatiotemporal evolution of the lattice dynamics dominated by local rotations with minor strain and shear contributions.
{"title":"Tailored nanophononic wavefield in a patterned bilayer system probed by ultrafast convergent beam electron diffraction","authors":"N. Bach, A. Feist, M. Möller, C. Ropers, S. Schäfer","doi":"10.1063/4.0000144","DOIUrl":"https://doi.org/10.1063/4.0000144","url":null,"abstract":"Optically excited nanostructures provide a versatile platform for the generation of confined nanophononic fields with potential (non-)linear interactions between different degrees of freedom. Control of resonance frequencies and the selective excitation of acoustic modes still remains challenging due to the interplay of nanoscale geometries and interfacial coupling mechanisms. Here, we demonstrate that a semiconductor membrane patterned with a platinum stripe acts as a tailored source for high-frequency strain waves generating a multi-modal distortion wave propagating through the membrane. To locally monitor the ultrafast structural dynamics at a specific distance from the deposited metal stripe, we employ ultrafast convergent beam electron diffraction in a laser-pump/electron-probe scheme. Experimentally observed acoustic deformations are reproduced by numerical simulations in a continuous medium model, revealing a spatiotemporal evolution of the lattice dynamics dominated by local rotations with minor strain and shear contributions.","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2022-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41437212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-28eCollection Date: 2022-03-01DOI: 10.1063/4.0000149
Qinda Guo, Maciej Dendzik, Antonija Grubišić-Čabo, Magnus H Berntsen, Cong Li, Wanyu Chen, Bharti Matta, Ulrich Starke, Björn Hessmo, Jonas Weissenrieder, Oscar Tjernberg
Here, we present a high repetition rate, narrow bandwidth, extreme ultraviolet photon source for time- and angle-resolved photoemission spectroscopy. The narrow bandwidth pulses meV for photon energies eV are generated through high harmonic generation using ultra-violet drive pulses with relatively long pulse lengths (461 fs). The high harmonic generation setup employs an annular drive beam in tight focusing geometry at a repetition rate of 250 kHz. Photon energy selection is provided by a series of selectable multilayer bandpass mirrors and thin film filters, thus avoiding any time broadening introduced by single grating monochromators. A two stage optical-parametric amplifier provides < 100 fs tunable pump pulses from 0.65 μm to 9 μm. The narrow bandwidth performance of the light source is demonstrated through angle-resolved photoemission measurements on a series of quantum materials, including high-temperature superconductor Bi-2212, WSe2, and graphene.
{"title":"A narrow bandwidth extreme ultra-violet light source for time- and angle-resolved photoemission spectroscopy.","authors":"Qinda Guo, Maciej Dendzik, Antonija Grubišić-Čabo, Magnus H Berntsen, Cong Li, Wanyu Chen, Bharti Matta, Ulrich Starke, Björn Hessmo, Jonas Weissenrieder, Oscar Tjernberg","doi":"10.1063/4.0000149","DOIUrl":"10.1063/4.0000149","url":null,"abstract":"<p><p>Here, we present a high repetition rate, narrow bandwidth, extreme ultraviolet photon source for time- and angle-resolved photoemission spectroscopy. The narrow bandwidth pulses <math><mrow><mo>Δ</mo> <mi>E</mi> <mo>=</mo> <mn>9</mn> <mo>,</mo> <mo> </mo> <mn>14</mn> <mo>,</mo> <mo> </mo> <mtext>and</mtext> <mo> </mo> <mn>18</mn></mrow> </math> meV for photon energies <math><mi>h</mi> <mi>ν</mi> <mo>=</mo> <mn>10.8</mn> <mo>,</mo> <mo> </mo> <mn>18.1</mn> <mo>,</mo> <mo> </mo> <mtext>and</mtext> <mo> </mo> <mn>25.3</mn></math> eV are generated through high harmonic generation using ultra-violet drive pulses with relatively long pulse lengths (461 fs). The high harmonic generation setup employs an annular drive beam in tight focusing geometry at a repetition rate of 250 kHz. Photon energy selection is provided by a series of selectable multilayer bandpass mirrors and thin film filters, thus avoiding any time broadening introduced by single grating monochromators. A two stage optical-parametric amplifier provides < 100 fs tunable pump pulses from 0.65 μm to 9 <i>μ</i>m. The narrow bandwidth performance of the light source is demonstrated through angle-resolved photoemission measurements on a series of quantum materials, including high-temperature superconductor Bi-2212, WSe<sub>2</sub>, and graphene.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2022-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9054270/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42599740","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-27eCollection Date: 2022-03-01DOI: 10.1063/4.0000141
T Teramoto, S Minemoto, T Majima, T Mizuno, J H Mun, A Yagishita, P Decleva, S Tsuru
Ultrafast x-ray photoelectron diffraction (UXPD) for free molecules has a promising potential to probe the local structures of the molecules in an element-specific fashion. Our UXPD scheme consists of three steps: (1) near-infrared laser (NIR) with ns pulse duration aligns sample molecules, (2) ultra-violet laser with fs pulse duration pumps the aligned molecules, and (3) soft x-ray free-electron laser (SXFEL) with fs pulse duration probes the molecules by measuring x-ray photoelectron diffraction (XPD) profiles. Employing steps of (1) and (3), we have measured I 3d XPD profiles from ground state iodobenzene aligned by the NIR laser with the SXFEL. Then, we have intensively calculated I 3d XPD profiles with density functional theory, taking degrees of alignments of the molecules into account, to extract a distance between C and I atoms in iodobenzene from the experimental I 3d XPD profiles. Although we have failed to determine the distance from the comparison between the experimental and theoretical results, we have succeeded in concluding that the degeneracies of the initial state eliminate the sensitivity on molecular structure in the I 3d XPD profiles. Thus, the observation of fine structures in the XPD profiles could be expected, if a nondegenerate molecular orbital is selected for a probe of UXPD. Finally, we have summarized our criteria to perform UXPD successfully: (1) to use SXFEL, (2) to prepare sample molecules with the degree of alignment higher than 0.8, and (3) to select a photoemission process from a nondegenerate inner-shell orbital of sample molecules.
自由分子的超快x射线光电子衍射(UXPD)在以特定元素的方式探测分子的局部结构方面具有很好的潜力。我们的UXPD方案包括三个步骤:(1)脉冲持续时间为ns的近红外激光(NIR)对准样品分子;(2)脉冲持续时间为fs的紫外激光泵浦对准分子;(3)脉冲持续时间为fs的软x射线自由电子激光(SXFEL)通过测量x射线光电子衍射(XPD)谱线探测分子。采用(1)和(3)的步骤,我们测量了近红外激光与SXFEL对准基态碘苯的I三维XPD剖面。然后,我们利用密度泛函理论集中计算了I - 3d XPD谱,考虑了分子的排列度,从实验I - 3d XPD谱中提取了碘苯中C和I原子之间的距离。虽然我们无法从实验和理论结果之间的比较中确定距离,但我们已经成功地得出结论,初始态的简并消除了三维XPD谱中分子结构的敏感性。因此,如果选择一个非简并的分子轨道作为UXPD探针,则可以预期在XPD剖面中观察到精细结构。最后,我们总结了成功进行UXPD的标准:(1)使用SXFEL,(2)制备取向度大于0.8的样品分子,(3)从样品分子的非简并内壳轨道选择光电过程。
{"title":"Basic studies toward ultrafast soft x-ray photoelectron diffraction; its application to probing local structure in iodobenzene molecules.","authors":"T Teramoto, S Minemoto, T Majima, T Mizuno, J H Mun, A Yagishita, P Decleva, S Tsuru","doi":"10.1063/4.0000141","DOIUrl":"10.1063/4.0000141","url":null,"abstract":"<p><p>Ultrafast x-ray photoelectron diffraction (UXPD) for free molecules has a promising potential to probe the local structures of the molecules in an element-specific fashion. Our UXPD scheme consists of three steps: (1) near-infrared laser (NIR) with ns pulse duration aligns sample molecules, (2) ultra-violet laser with fs pulse duration pumps the aligned molecules, and (3) soft x-ray free-electron laser (SXFEL) with fs pulse duration probes the molecules by measuring x-ray photoelectron diffraction (XPD) profiles. Employing steps of (1) and (3), we have measured <i>I</i> 3<i>d</i> XPD profiles from ground state iodobenzene aligned by the NIR laser with the SXFEL. Then, we have intensively calculated <i>I</i> 3<i>d</i> XPD profiles with density functional theory, taking degrees of alignments of the molecules into account, to extract a distance between <i>C</i> and <i>I</i> atoms in iodobenzene from the experimental <i>I</i> 3<i>d</i> XPD profiles. Although we have failed to determine the distance from the comparison between the experimental and theoretical results, we have succeeded in concluding that the degeneracies of the initial state eliminate the sensitivity on molecular structure in the <i>I</i> 3<i>d</i> XPD profiles. Thus, the observation of fine structures in the XPD profiles could be expected, if a nondegenerate molecular orbital is selected for a probe of UXPD. Finally, we have summarized our criteria to perform UXPD successfully: (1) to use SXFEL, (2) to prepare sample molecules with the degree of alignment higher than 0.8, and (3) to select a photoemission process from a nondegenerate inner-shell orbital of sample molecules.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2022-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9050171/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48597392","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-03-18eCollection Date: 2022-03-01DOI: 10.1063/4.0000138
W H Li, C J R Duncan, M B Andorf, A C Bartnik, E Bianco, L Cultrera, A Galdi, M Gordon, M Kaemingk, C A Pennington, L F Kourkoutis, I V Bazarov, J M Maxson
We report the design and performance of a time-resolved electron diffraction apparatus capable of producing intense bunches with simultaneously single digit micrometer probe size, long coherence length, and 200 fs rms time resolution. We measure the 5d (peak) beam brightness at the sample location in micro-diffraction mode to be . To generate high brightness electron bunches, the system employs high efficiency, low emittance semiconductor photocathodes driven with a wavelength near the photoemission threshold at a repetition rate up to 250 kHz. We characterize spatial, temporal, and reciprocal space resolution of the apparatus. We perform proof-of-principle measurements of ultrafast heating in single crystal Au samples and compare experimental results with simulations that account for the effects of multiple scattering.
{"title":"A kiloelectron-volt ultrafast electron micro-diffraction apparatus using low emittance semiconductor photocathodes.","authors":"W H Li, C J R Duncan, M B Andorf, A C Bartnik, E Bianco, L Cultrera, A Galdi, M Gordon, M Kaemingk, C A Pennington, L F Kourkoutis, I V Bazarov, J M Maxson","doi":"10.1063/4.0000138","DOIUrl":"10.1063/4.0000138","url":null,"abstract":"<p><p>We report the design and performance of a time-resolved electron diffraction apparatus capable of producing intense bunches with simultaneously single digit micrometer probe size, long coherence length, and 200 fs rms time resolution. We measure the 5d (peak) beam brightness at the sample location in micro-diffraction mode to be <math><mrow><mn>7</mn> <mo>×</mo> <msup><mrow><mn>10</mn></mrow> <mrow><mn>13</mn></mrow> </msup> <mo> </mo> <mi>A</mi> <mo>/</mo> <msup><mi>m</mi> <mn>2</mn></msup> <mo> </mo> <msup><mrow><mtext>rad</mtext></mrow> <mn>2</mn></msup> </mrow> </math> . To generate high brightness electron bunches, the system employs high efficiency, low emittance semiconductor photocathodes driven with a wavelength near the photoemission threshold at a repetition rate up to 250 kHz. We characterize spatial, temporal, and reciprocal space resolution of the apparatus. We perform proof-of-principle measurements of ultrafast heating in single crystal Au samples and compare experimental results with simulations that account for the effects of multiple scattering.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2022-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8934190/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48984107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-03-14eCollection Date: 2022-03-01DOI: 10.1063/4.0000133
M P Jiang, S Fahy, A Hauber, É D Murray, I Savić, C Bray, J N Clark, T Henighan, M Kozina, A M Lindenberg, P Zalden, M Chollet, J M Glownia, M C Hoffmann, T Sato, D Zhu, O Delaire, A F May, B C Sales, R Merlin, M Trigo, D A Reis
We report the observation of photo-induced plasmon-phonon coupled modes in the group IV-VI semiconductor PbTe using ultrafast x-ray diffuse scattering at the Linac Coherent Light Source. We measure the near-zone-center excited-state dispersion of the heavily screened longitudinal optical (LO) phonon branch as extracted from differential changes in x-ray diffuse scattering intensity following above bandgap photoexcitation. We suggest that upon photoexcitation, the LO phonon-plasmon coupled (LOPC) modes themselves become coupled to longitudinal acoustic modes that drive electron band shifts via acoustic deformation potentials and possibly to low-energy single-particle excitations within the plasma and that these couplings give rise to displacement-correlations that oscillate in time with a period given effectively by the heavily screened LOPC frequency.
{"title":"Observation of photo-induced plasmon-phonon coupling in PbTe via ultrafast x-ray scattering.","authors":"M P Jiang, S Fahy, A Hauber, É D Murray, I Savić, C Bray, J N Clark, T Henighan, M Kozina, A M Lindenberg, P Zalden, M Chollet, J M Glownia, M C Hoffmann, T Sato, D Zhu, O Delaire, A F May, B C Sales, R Merlin, M Trigo, D A Reis","doi":"10.1063/4.0000133","DOIUrl":"https://doi.org/10.1063/4.0000133","url":null,"abstract":"<p><p>We report the observation of photo-induced plasmon-phonon coupled modes in the group IV-VI semiconductor PbTe using ultrafast x-ray diffuse scattering at the Linac Coherent Light Source. We measure the near-zone-center excited-state dispersion of the heavily screened longitudinal optical (LO) phonon branch as extracted from differential changes in x-ray diffuse scattering intensity following above bandgap photoexcitation. We suggest that upon photoexcitation, the LO phonon-plasmon coupled (LOPC) modes themselves become coupled to longitudinal acoustic modes that drive electron band shifts via acoustic deformation potentials and possibly to low-energy single-particle excitations within the plasma and that these couplings give rise to displacement-correlations that oscillate in time with a period given effectively by the heavily screened LOPC frequency.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2022-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8923709/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"40308673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-03-08eCollection Date: 2022-03-01DOI: 10.1063/4.0000143
Isabel Gonzalez-Vallejo, Azize Koç, Klaus Reimann, Michael Woerner, Thomas Elsaesser
Soft modes in crystals are lattice vibrations with frequencies that decrease and eventually vanish as the temperature approaches a critical point, e.g., a structural change due to a phase transition. In ionic para- or ferroelectric materials, the frequency decrease is connected with a diverging electric susceptibility and, for infrared active modes, a strong increase in oscillator strength. The traditional picture describes soft modes as overdamped transverse optical phonons of a hybrid vibrational-electronic character. In this context, potassium dihydrogen phosphate (KH2PO4, KDP) has been studied for decades as a prototypical material with, however, inconclusive results regarding the soft modes in its para- and ferroelectric phase. There are conflicting assignments of soft-mode frequencies and damping parameters. We report the first observation of a longitudinal underdamped soft mode in paraelectric KDP. Upon impulsive femtosecond Raman excitation of coherent low-frequency phonons in the electronic ground state of KDP crystallites, transient powder diffraction patterns are recorded with femtosecond hard x-ray pulses. Electron density maps derived from the x-ray data reveal oscillatory charge relocations over interatomic distances, much larger than the sub-picometer nuclear displacements, a direct hallmark of soft-mode behavior. The strongly underdamped character of the soft mode manifests in charge oscillations persisting for more than 10 ps. The soft-mode frequency decreases from 0.55 THz at T =295 K to 0.39 THz at T =175 K. An analysis of the Raman excitation conditions in crystallites and the weak damping demonstrate a longitudinal character. Our results extend soft-mode physics well beyond the traditional picture and pave the way for an atomic-level characterization of soft modes.
{"title":"Underdamped longitudinal soft modes in ionic crystallites-lattice and charge motions observed by ultrafast x-ray diffraction.","authors":"Isabel Gonzalez-Vallejo, Azize Koç, Klaus Reimann, Michael Woerner, Thomas Elsaesser","doi":"10.1063/4.0000143","DOIUrl":"https://doi.org/10.1063/4.0000143","url":null,"abstract":"<p><p>Soft modes in crystals are lattice vibrations with frequencies that decrease and eventually vanish as the temperature approaches a critical point, e.g., a structural change due to a phase transition. In ionic para- or ferroelectric materials, the frequency decrease is connected with a diverging electric susceptibility and, for infrared active modes, a strong increase in oscillator strength. The traditional picture describes soft modes as overdamped transverse optical phonons of a hybrid vibrational-electronic character. In this context, potassium dihydrogen phosphate (KH<sub>2</sub>PO<sub>4</sub>, KDP) has been studied for decades as a prototypical material with, however, inconclusive results regarding the soft modes in its para- and ferroelectric phase. There are conflicting assignments of soft-mode frequencies and damping parameters. We report the first observation of a longitudinal underdamped soft mode in paraelectric KDP. Upon impulsive femtosecond Raman excitation of coherent low-frequency phonons in the electronic ground state of KDP crystallites, transient powder diffraction patterns are recorded with femtosecond hard x-ray pulses. Electron density maps derived from the x-ray data reveal oscillatory charge relocations over interatomic distances, much larger than the sub-picometer nuclear displacements, a direct hallmark of soft-mode behavior. The strongly underdamped character of the soft mode manifests in charge oscillations persisting for more than 10 ps. The soft-mode frequency decreases from 0.55 THz at <i>T </i>=<i> </i>295 K to 0.39 THz at <i>T </i>=<i> </i>175 K. An analysis of the Raman excitation conditions in crystallites and the weak damping demonstrate a longitudinal character. Our results extend soft-mode physics well beyond the traditional picture and pave the way for an atomic-level characterization of soft modes.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2022-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8906907/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"40309605","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-02-24eCollection Date: 2022-01-01DOI: 10.1063/4.0000131
I Gonzalez-Vallejo, V L R Jacques, D Boschetto, G Rizza, A Hadj-Azzem, J Faure, D Le Bolloc'h
We use ultrafast electron diffraction to study the out-of-equilibrium dynamics of the charge density wave (CDW) phase transition in GdTe3, a quasi-two-dimensional compound displaying a unidirectional CDW state. Experiments were conducted at different incident fluences and different initial sample temperatures below Tc. We find that following photo-excitation, the system undergoes a non-thermal ultrafast phase transition that occurs in out-of-equilibrium conditions. The intrinsic crystal temperature was estimated at each time delay from the atomic thermal motion, which affects each Bragg peak intensity via the Debye Waller factor. We find that the crystal temperature stabilizes with a 6 ps timescale in a quasi-equilibrium state at temperature . We then relate the recovery time of the CDW and its correlation lengths as a function of . The charge density wave is suppressed in less than a picosecond while its recovery time increases linearly with incident fluence and initial temperature. Our results highlight that the dynamics is strongly determined by the initial sample temperature. In addition, the transient CDW phase recently observed along the transverse direction in LaTe3 and CeTe3 is not observed in GdTe3.
{"title":"Time-resolved structural dynamics of the out-of-equilibrium charge density wave phase transition in GdTe<sub>3</sub>.","authors":"I Gonzalez-Vallejo, V L R Jacques, D Boschetto, G Rizza, A Hadj-Azzem, J Faure, D Le Bolloc'h","doi":"10.1063/4.0000131","DOIUrl":"10.1063/4.0000131","url":null,"abstract":"<p><p>We use ultrafast electron diffraction to study the out-of-equilibrium dynamics of the charge density wave (CDW) phase transition in GdTe<sub>3</sub>, a quasi-two-dimensional compound displaying a unidirectional CDW state. Experiments were conducted at different incident fluences and different initial sample temperatures below T<sub><i>c</i></sub>. We find that following photo-excitation, the system undergoes a non-thermal ultrafast phase transition that occurs in out-of-equilibrium conditions. The intrinsic crystal temperature was estimated at each time delay from the atomic thermal motion, which affects each Bragg peak intensity via the Debye Waller factor. We find that the crystal temperature stabilizes with a 6 ps timescale in a quasi-equilibrium state at temperature <math><mrow><msub><mi>T</mi><mrow><mi>q</mi><mo>.</mo><mi>e</mi><mo>.</mo></mrow></msub></mrow></math>. We then relate the recovery time of the CDW and its correlation lengths as a function of <math><mrow><msub><mi>T</mi><mrow><mi>q</mi><mo>.</mo><mi>e</mi><mo>.</mo></mrow></msub></mrow></math>. The charge density wave is suppressed in less than a picosecond while its recovery time increases linearly with incident fluence and initial temperature. Our results highlight that the dynamics is strongly determined by the initial sample temperature. In addition, the transient CDW phase recently observed along the transverse direction in LaTe<sub>3</sub> and CeTe<sub>3</sub> is not observed in GdTe<sub>3</sub>.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2022-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10748500/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46244898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-13eCollection Date: 2022-01-01DOI: 10.1063/4.0000134
Giovanni Pica, Daniele Bajoni, Giulia Grancini
Electro-optical spectroscopy is nowadays a routine approach for the analysis of light induced properties and dynamical processes in matter, whose understanding is particularly crucial for the intelligent design of novel synthetic materials and the engineering and optimization of high-impact optoelectronic devices. Currently, within this field, it is the common choice to rely on multiple commercial setups, often costly and complex, which can rarely combine multiple functions at the same time with the required sensitivity, resolution, and spectral tunability (in both excitation and detection). Here, we present an innovative, compact, and low-cost system based on "three in one" components for the simultaneous electro-optical material and device characterization. It relies on compact fiber-coupled Fourier transform spectroscopy, the core of the system, enabling a fast spectral analysis to acquire simultaneously wavelength and time resolved photoluminescence (PL) maps (as a function of the time and wavelength), PL quantum yield, and electroluminescence signal. Our system bypasses conventional ones, proposing a new solution for a compact, low-cost, and user-friendly tool, while maintaining high levels of resolution and sensitivity.
{"title":"A step beyond in steady-state and time-resolved electro-optical spectroscopy: Demonstration of a customized simple, compact, low-cost, fiber-based interferometer system.","authors":"Giovanni Pica, Daniele Bajoni, Giulia Grancini","doi":"10.1063/4.0000134","DOIUrl":"https://doi.org/10.1063/4.0000134","url":null,"abstract":"<p><p>Electro-optical spectroscopy is nowadays a routine approach for the analysis of light induced properties and dynamical processes in matter, whose understanding is particularly crucial for the intelligent design of novel synthetic materials and the engineering and optimization of high-impact optoelectronic devices. Currently, within this field, it is the common choice to rely on multiple commercial setups, often costly and complex, which can rarely combine multiple functions at the same time with the required sensitivity, resolution, and spectral tunability (in both excitation and detection). Here, we present an innovative, compact, and low-cost system based on \"three in one\" components for the simultaneous electro-optical material and device characterization. It relies on compact fiber-coupled Fourier transform spectroscopy, the core of the system, enabling a fast spectral analysis to acquire simultaneously wavelength and time resolved photoluminescence (PL) maps (as a function of the time and wavelength), PL quantum yield, and electroluminescence signal. Our system bypasses conventional ones, proposing a new solution for a compact, low-cost, and user-friendly tool, while maintaining high levels of resolution and sensitivity.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2022-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8759798/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39943744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-13eCollection Date: 2022-01-01DOI: 10.1063/4.0000132
Yingchao Zhang, Xun Shi, Mengxue Guan, Wenjing You, Yigui Zhong, Tika R Kafle, Yaobo Huang, Hong Ding, Michael Bauer, Kai Rossnagel, Sheng Meng, Henry C Kapteyn, Margaret M Murnane
Charge density wave (CDW) order is an emergent quantum phase that is characterized by periodic lattice distortion and charge density modulation, often present near superconducting transitions. Here, we uncover a novel inverted CDW state by using a femtosecond laser to coherently reverse the star-of-David lattice distortion in 1T-TaSe2. We track the signature of this novel CDW state using time- and angle-resolved photoemission spectroscopy and the time-dependent density functional theory to validate that it is associated with a unique lattice and charge arrangement never before realized. The dynamic electronic structure further reveals its novel properties that are characterized by an increased density of states near the Fermi level, high metallicity, and altered electron-phonon couplings. Our results demonstrate how ultrafast lasers can be used to create unique states in materials by manipulating charge-lattice orders and couplings.
{"title":"Creation of a novel inverted charge density wave state.","authors":"Yingchao Zhang, Xun Shi, Mengxue Guan, Wenjing You, Yigui Zhong, Tika R Kafle, Yaobo Huang, Hong Ding, Michael Bauer, Kai Rossnagel, Sheng Meng, Henry C Kapteyn, Margaret M Murnane","doi":"10.1063/4.0000132","DOIUrl":"https://doi.org/10.1063/4.0000132","url":null,"abstract":"<p><p>Charge density wave (CDW) order is an emergent quantum phase that is characterized by periodic lattice distortion and charge density modulation, often present near superconducting transitions. Here, we uncover a novel inverted CDW state by using a femtosecond laser to coherently reverse the star-of-David lattice distortion in 1<i>T</i>-TaSe<sub>2</sub>. We track the signature of this novel CDW state using time- and angle-resolved photoemission spectroscopy and the time-dependent density functional theory to validate that it is associated with a unique lattice and charge arrangement never before realized. The dynamic electronic structure further reveals its novel properties that are characterized by an increased density of states near the Fermi level, high metallicity, and altered electron-phonon couplings. Our results demonstrate how ultrafast lasers can be used to create unique states in materials by manipulating charge-lattice orders and couplings.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2022-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8759797/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39943746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}