Pub Date : 2020-12-01DOI: 10.1103/PhysRevB.103.195148
A. Dontsov, A. Dmitriev
In this paper we consider analytically the density evolution of a spinless Fermi liquid with nonlinear dispersion into which one particle is injected. The liquid interaction is point-like and the temperature is zero. We obtain a formula for the evolution of the density deviation and discuss the picture it gives as well as the physics behind it. We find further fractionalization of the initial density hump comparing to the linear dispersion case: it splits into three humps instead of two. All three change their shapes in a complicated sort of way, and we analyse the mechanisms of these phenomena. We also show that the fractionalization can be illustrated from a semiclassical point of view.
{"title":"Charge fractionalization beyond the Luttinger liquid paradigm: An analytical consideration","authors":"A. Dontsov, A. Dmitriev","doi":"10.1103/PhysRevB.103.195148","DOIUrl":"https://doi.org/10.1103/PhysRevB.103.195148","url":null,"abstract":"In this paper we consider analytically the density evolution of a spinless Fermi liquid with nonlinear dispersion into which one particle is injected. The liquid interaction is point-like and the temperature is zero. We obtain a formula for the evolution of the density deviation and discuss the picture it gives as well as the physics behind it. We find further fractionalization of the initial density hump comparing to the linear dispersion case: it splits into three humps instead of two. All three change their shapes in a complicated sort of way, and we analyse the mechanisms of these phenomena. We also show that the fractionalization can be illustrated from a semiclassical point of view.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83765828","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-01DOI: 10.1103/PHYSREVMATERIALS.5.034401
S. Curley, R. Scatena, R. C. Williams, P. Goddard, P. Macchi, T. J. Hicken, T. Lancaster, F. Xiao, S. Blundell, V. Zapf, J. Eckert, E. Krenkel, J. Villa, M. Rhodehouse, J. Manson
The magnetic properties of the two isostructural molecule-based magnets, Ni(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 1, [thiourea = SC(NH$_2$)$_2$] and Co(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 3/2, are characterised using several techniques in order to rationalise their relationship with structural parameters and ascertain magnetic changes caused by substitution of the spin. Zero-field heat capacity and muon-spin relaxation measurements reveal low-temperature long-range ordering in both compounds, in addition to Ising-like ($D < 0$) single-ion anisotropy ($D_{rm{Co}} sim$ -100 K, $D_{rm{Ni}} sim$ -10 K). Crystal and electronic structure, combined with DC-field magnetometry, affirm highly quasi-one-dimensional behaviour, with ferromagnetic intrachain exchange interactions $J_{rm{Co}}approx+4$ K and $J_{rm{Ni}}sim+100$ K and weak antiferromagnetic interchain exchange, on the order of $J'$ $sim-0.1$ K. Electron charge and spin-density mapping reveals through-space exchange as a mechanism to explain the large discrepancy in $J$-values despite, from a structural perspective, the highly similar exchange pathways in both materials. Both species can be compared to the similar compounds $M$Cl$_2$(thiourea)$_4$, $M$ = Ni(II) (DTN) and Co(II) (DTC), where DTN is know to harbour two magnetic field-induced quantum critical points. Direct comparison of DTN and DTC with the compounds studied here shows that substituting the halide Cl$^-$ ion, for the NCS$^-$ ion, results in a dramatic change in both the structural and magnetic properties.
{"title":"Magnetic ground state of the one-dimensional ferromagnetic chain compoundsM(NCS)2(thiourea)2(M=Ni,Co)","authors":"S. Curley, R. Scatena, R. C. Williams, P. Goddard, P. Macchi, T. J. Hicken, T. Lancaster, F. Xiao, S. Blundell, V. Zapf, J. Eckert, E. Krenkel, J. Villa, M. Rhodehouse, J. Manson","doi":"10.1103/PHYSREVMATERIALS.5.034401","DOIUrl":"https://doi.org/10.1103/PHYSREVMATERIALS.5.034401","url":null,"abstract":"The magnetic properties of the two isostructural molecule-based magnets, Ni(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 1, [thiourea = SC(NH$_2$)$_2$] and Co(NCS)$_{2}$(thiourea)$_{2}$, $S$ = 3/2, are characterised using several techniques in order to rationalise their relationship with structural parameters and ascertain magnetic changes caused by substitution of the spin. Zero-field heat capacity and muon-spin relaxation measurements reveal low-temperature long-range ordering in both compounds, in addition to Ising-like ($D < 0$) single-ion anisotropy ($D_{rm{Co}} sim$ -100 K, $D_{rm{Ni}} sim$ -10 K). Crystal and electronic structure, combined with DC-field magnetometry, affirm highly quasi-one-dimensional behaviour, with ferromagnetic intrachain exchange interactions $J_{rm{Co}}approx+4$ K and $J_{rm{Ni}}sim+100$ K and weak antiferromagnetic interchain exchange, on the order of $J'$ $sim-0.1$ K. Electron charge and spin-density mapping reveals through-space exchange as a mechanism to explain the large discrepancy in $J$-values despite, from a structural perspective, the highly similar exchange pathways in both materials. Both species can be compared to the similar compounds $M$Cl$_2$(thiourea)$_4$, $M$ = Ni(II) (DTN) and Co(II) (DTC), where DTN is know to harbour two magnetic field-induced quantum critical points. Direct comparison of DTN and DTC with the compounds studied here shows that substituting the halide Cl$^-$ ion, for the NCS$^-$ ion, results in a dramatic change in both the structural and magnetic properties.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"49 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91431623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-11-30DOI: 10.1103/PhysRevB.103.205112
Y. Yanagi, J. Ikeda, K. Fujiwara, K. Nomura, A. Tsukazaki, Michi-To Suzuki
Co-based shandite Co$_3$Sn$_2$S$_2$ is a representative example of magnetic Weyl semimetals showing rich transport phenomena. We thoroughly investigate magnetic and transport properties of hole-doped shandites Co$_3$In$_x$Sn$_{2-x}$S$_2$ by first-principles calculations. The calculations reproduce nonlinear reduction of anomalous Hall conductivity with doping In for Co$_3$Sn$_2$S$_2$, as reported in experiments, against the linearly decreased ferromagnetic moment within virtual crystal approximation. We show that a drastic change in the band parity character of Fermi surfaces, attributed to the nodal rings lifted energetically with In-doping, leads to strong enhancement of anomalous Nernst conductivity with reversing its sign in Co$_3$In$_x$Sn$_{2-x}$S$_2$.
Co-based shan - ite Co$_3$Sn$_2$S$_2$是具有丰富输运现象的磁性Weyl半金属的代表。用第一性原理计算方法研究了空穴掺杂山质岩Co$_3$In$_x$Sn$_{2-x}$S$_2$的磁性和输运性质。计算重现了在Co$_3$Sn$_2$S$_2$中掺杂In对反常霍尔电导率的非线性降低，与实验报道的相反，在虚晶体近似下铁磁矩线性降低。我们发现，在Co$_3$ in $_x$Sn$_{2-x}$S$_2$中掺杂的节点环能量提升导致费米表面的能带宇称特性发生了剧烈的变化，反常能司特电导率在Co$_3$ in $_x$Sn$ _2$中发生了反转。
{"title":"First-principles investigation of magnetic and transport properties in hole-doped shandite compounds \u0000Co3InxSn2−xS2","authors":"Y. Yanagi, J. Ikeda, K. Fujiwara, K. Nomura, A. Tsukazaki, Michi-To Suzuki","doi":"10.1103/PhysRevB.103.205112","DOIUrl":"https://doi.org/10.1103/PhysRevB.103.205112","url":null,"abstract":"Co-based shandite Co$_3$Sn$_2$S$_2$ is a representative example of magnetic Weyl semimetals showing rich transport phenomena. We thoroughly investigate magnetic and transport properties of hole-doped shandites Co$_3$In$_x$Sn$_{2-x}$S$_2$ by first-principles calculations. The calculations reproduce nonlinear reduction of anomalous Hall conductivity with doping In for Co$_3$Sn$_2$S$_2$, as reported in experiments, against the linearly decreased ferromagnetic moment within virtual crystal approximation. We show that a drastic change in the band parity character of Fermi surfaces, attributed to the nodal rings lifted energetically with In-doping, leads to strong enhancement of anomalous Nernst conductivity with reversing its sign in Co$_3$In$_x$Sn$_{2-x}$S$_2$.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"48 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78632204","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-11-29DOI: 10.1103/PHYSREVB.103.L121104
J. Nasu, M. Naka
We propose a mechanism of the spin Seebeck effect attributed to excitonic condensation in a nonmagnetic insulator. We analyze a half-filled two-orbital Hubbard model with a crystalline field splitting in the strong coupling limit. In this model, the competition between the crystalline field and electron correlations brings about an excitonic insulating state, where the two orbitals are spontaneously hybridized. Using the generalized spin-wave theory and Boltzmann transport equation, we find that a spin current generated by a thermal gradient is observed in the excitonic insulating state without magnetic fields. The spin Seebeck effect originates from spin-split collective excitation modes although the ground state does not exhibit any magnetic orderings. This peculiar phenomenon is inherent in the excitonic insulating state, whose order parameter is time-reversal odd and yields a spin splitting for the collective excitation modes. We also find that the spin current is strongly enhanced and its direction is inverted in the vicinity of the phase transition to another magnetically ordered phase. We suggest that the present phenomenon is possibly observed in perovskite cobaltites with the GdFeO$_3$-type lattice distortion.
{"title":"Spin Seebeck effect in nonmagnetic excitonic insulators","authors":"J. Nasu, M. Naka","doi":"10.1103/PHYSREVB.103.L121104","DOIUrl":"https://doi.org/10.1103/PHYSREVB.103.L121104","url":null,"abstract":"We propose a mechanism of the spin Seebeck effect attributed to excitonic condensation in a nonmagnetic insulator. We analyze a half-filled two-orbital Hubbard model with a crystalline field splitting in the strong coupling limit. In this model, the competition between the crystalline field and electron correlations brings about an excitonic insulating state, where the two orbitals are spontaneously hybridized. Using the generalized spin-wave theory and Boltzmann transport equation, we find that a spin current generated by a thermal gradient is observed in the excitonic insulating state without magnetic fields. The spin Seebeck effect originates from spin-split collective excitation modes although the ground state does not exhibit any magnetic orderings. This peculiar phenomenon is inherent in the excitonic insulating state, whose order parameter is time-reversal odd and yields a spin splitting for the collective excitation modes. We also find that the spin current is strongly enhanced and its direction is inverted in the vicinity of the phase transition to another magnetically ordered phase. We suggest that the present phenomenon is possibly observed in perovskite cobaltites with the GdFeO$_3$-type lattice distortion.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84058019","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-11-27DOI: 10.1103/PhysRevB.103.L241110
Nicol'as Morales-Dur'an, A. Macdonald, P. Potasz
Moir'e superlattices formed in two-dimensional semiconductor heterobilayers provide a new realization of Hubbard model physics in which the number of electrons per effective atom can be tuned at will. We report on an exact diagonalization study of the electronic properties of half-filled narrow moir'e bands in which correlation strengths are varied by changing twist angles or interaction strengths. We construct a phase diagram for the bilayer, identifying where the metal-insulator phase transition occurs, estimating the sizes of the charge gaps in the insulating phase, and commenting on the nature of the transition.
{"title":"Metal-insulator transition in transition metal dichalcogenide heterobilayer moiré superlattices","authors":"Nicol'as Morales-Dur'an, A. Macdonald, P. Potasz","doi":"10.1103/PhysRevB.103.L241110","DOIUrl":"https://doi.org/10.1103/PhysRevB.103.L241110","url":null,"abstract":"Moir'e superlattices formed in two-dimensional semiconductor heterobilayers provide a new realization of Hubbard model physics in which the number of electrons per effective atom can be tuned at will. We report on an exact diagonalization study of the electronic properties of half-filled narrow moir'e bands in which correlation strengths are varied by changing twist angles or interaction strengths. We construct a phase diagram for the bilayer, identifying where the metal-insulator phase transition occurs, estimating the sizes of the charge gaps in the insulating phase, and commenting on the nature of the transition.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"105 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76139133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-11-25DOI: 10.1103/PHYSREVB.103.054422
S. Hayami, Y. Motome
We theoretically investigate multiple-$Q$ spin textures, which are composed of superpositions of spin density waves with different wave numbers, for an effective spin model of centrosymmetric itinerant magnets. Our focus is on the interplay between biquadratic interactions arising from the spin-charge coupling and magnetic anisotropy caused by the spin-orbit coupling. Taking into account two types of the magnetic anisotropy, single-ion anisotropy and bond-dependent anisotropy, we elucidate magnetic phase diagrams for an archetypal triangular-lattice system in the absence and presence of an external magnetic field. In the case of the single-ion anisotropy, we find a plethora of multiple-$Q$ instabilities depending on the strength and the sign of the anisotropy (easy plane or easy axis), including a skyrmion crystal with topological number of two. In an external magnetic field, we find that a skyrmion crystal with topological number of one is stabilized by the in-plane (out-of-plane) magnetic field under the easy-plane (easy-axis) anisotropy. We also examine the stability of the field-induced skyrmion crystal by rotating the field direction. As a biproduct, we show that a meron crystal with the skyrmion number of one half appears in the presence of the biquadratic interaction and the easy-axis anisotropy. Meanwhile, we find that the bond-dependent anisotropy also stabilizes both types of skyrmion crystals. We show that, however, for the skyrmion crystal with topological number of one, Bloch- and Neel-type skyrmion crystals are selectively realized depending on the sign of the bond-dependent anisotropy. Moreover, we find yet another multiple-$Q$ states, including a meron crystal and a double meron crystal with the skyrmion number of one. The systematic investigation will provide a reference to complex magnetic textures in centrosymmetric magnetic metals.
{"title":"Noncoplanar multiple-\u0000Q\u0000 spin textures by itinerant frustration: Effects of single-ion anisotropy and bond-dependent anisotropy","authors":"S. Hayami, Y. Motome","doi":"10.1103/PHYSREVB.103.054422","DOIUrl":"https://doi.org/10.1103/PHYSREVB.103.054422","url":null,"abstract":"We theoretically investigate multiple-$Q$ spin textures, which are composed of superpositions of spin density waves with different wave numbers, for an effective spin model of centrosymmetric itinerant magnets. Our focus is on the interplay between biquadratic interactions arising from the spin-charge coupling and magnetic anisotropy caused by the spin-orbit coupling. Taking into account two types of the magnetic anisotropy, single-ion anisotropy and bond-dependent anisotropy, we elucidate magnetic phase diagrams for an archetypal triangular-lattice system in the absence and presence of an external magnetic field. In the case of the single-ion anisotropy, we find a plethora of multiple-$Q$ instabilities depending on the strength and the sign of the anisotropy (easy plane or easy axis), including a skyrmion crystal with topological number of two. In an external magnetic field, we find that a skyrmion crystal with topological number of one is stabilized by the in-plane (out-of-plane) magnetic field under the easy-plane (easy-axis) anisotropy. We also examine the stability of the field-induced skyrmion crystal by rotating the field direction. As a biproduct, we show that a meron crystal with the skyrmion number of one half appears in the presence of the biquadratic interaction and the easy-axis anisotropy. Meanwhile, we find that the bond-dependent anisotropy also stabilizes both types of skyrmion crystals. We show that, however, for the skyrmion crystal with topological number of one, Bloch- and Neel-type skyrmion crystals are selectively realized depending on the sign of the bond-dependent anisotropy. Moreover, we find yet another multiple-$Q$ states, including a meron crystal and a double meron crystal with the skyrmion number of one. The systematic investigation will provide a reference to complex magnetic textures in centrosymmetric magnetic metals.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"47 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90427331","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-11-24DOI: 10.21468/SCIPOSTPHYS.10.4.087
R. Rausch, Cassian Plorin, M. Peschke
We solve the quantum-mechanical antiferromagnetic Heisenberg model with spins positioned on vertices of the truncated icosahedron using the density-matrix renormalization group (DMRG). This describes magnetic properties of the undoped C$_{60}$ fullerene at half filling in the limit of strong on-site interaction $U$. We calculate the ground state and correlation functions for all possible distances, the lowest singlet and triplet excited states, as well as thermodynamic properties, namely the specific heat and spin susceptibility. We find that unlike the exactly solvable C$_{20}$ to C$_{32}$, the lowest excited state is a triplet rather than a singlet, indicating a reduced frustration due to the presence of many hexagon faces and the separation of the pentagon faces. This implies that frustration may be tuneable within the fullerenes by changing their size. The spin-spin correlations are much stronger along the hexagon bonds and rapidly decrease with distance, so that the molecule is large enough not to be correlated across its whole extent. The specific heat shows a high-temperature peak and a low-temperature shoulder reminiscent of the Kagom'e lattice, while the spin susceptibility shows a single broad peak and is very close to the one of C$_{20}$.
{"title":"The antiferromagnetic $S=1/2$ Heisenberg model on the C$_{60}$ fullerene geometry","authors":"R. Rausch, Cassian Plorin, M. Peschke","doi":"10.21468/SCIPOSTPHYS.10.4.087","DOIUrl":"https://doi.org/10.21468/SCIPOSTPHYS.10.4.087","url":null,"abstract":"We solve the quantum-mechanical antiferromagnetic Heisenberg model with spins positioned on vertices of the truncated icosahedron using the density-matrix renormalization group (DMRG). This describes magnetic properties of the undoped C$_{60}$ fullerene at half filling in the limit of strong on-site interaction $U$. We calculate the ground state and correlation functions for all possible distances, the lowest singlet and triplet excited states, as well as thermodynamic properties, namely the specific heat and spin susceptibility. We find that unlike the exactly solvable C$_{20}$ to C$_{32}$, the lowest excited state is a triplet rather than a singlet, indicating a reduced frustration due to the presence of many hexagon faces and the separation of the pentagon faces. This implies that frustration may be tuneable within the fullerenes by changing their size. The spin-spin correlations are much stronger along the hexagon bonds and rapidly decrease with distance, so that the molecule is large enough not to be correlated across its whole extent. The specific heat shows a high-temperature peak and a low-temperature shoulder reminiscent of the Kagom'e lattice, while the spin susceptibility shows a single broad peak and is very close to the one of C$_{20}$.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"27 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82503214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-11-24DOI: 10.1103/physrevb.102.195145
Gunnar Bollmark, N. Laflorencie, A. Kantian
Quasi-one-dimensional (Q1D) systems, i.e., three- and two-dimensional (3D/2D) arrays composed of weakly coupled one-dimensional lattices of interacting quantum particles, exhibit rich and fascinating physics. They are studied across various areas of condensed matter and ultracold atomic lattice-gas physics, and are often marked by dimensional crossover as the coupling between one-dimensional systems is increased or temperature decreased, i.e., the Q1D system goes from appearing largely 1D to largely 3D. Phase transitions occurring along the crossover can strongly enhance this effect. Understanding these crossovers and associated phase transitions can be challenging due to the very different elementary excitations of 1D systems compared to higher-dimensional ones. In the present work, we combine numerical matrix product state (MPS) methods with mean-field (MF) theory to study paradigmatic cases of dimensional crossovers and the associated phase transitions in systems of both hard-core and soft-core lattice bosons, with relevance to both condensed matter physics and ultracold atomic gases. We show that the superfluid-to-insulator transition is a first order one, as opposed to the isotropic cases and calculate transition temperatures for the superfluid states, finding excellent agreement with analytical theory. At the same time, our MPS+MF approach keeps functioning well where the current analytical framework cannot be applied. We further confirm the qualitative and quantitative reliability of our approach by comparison to exact quantum Monte Carlo calculations for the full 3D arrays.
{"title":"Dimensional crossover and phase transitions in coupled chains: Density matrix renormalization group results","authors":"Gunnar Bollmark, N. Laflorencie, A. Kantian","doi":"10.1103/physrevb.102.195145","DOIUrl":"https://doi.org/10.1103/physrevb.102.195145","url":null,"abstract":"Quasi-one-dimensional (Q1D) systems, i.e., three- and two-dimensional (3D/2D) arrays composed of weakly coupled one-dimensional lattices of interacting quantum particles, exhibit rich and fascinating physics. They are studied across various areas of condensed matter and ultracold atomic lattice-gas physics, and are often marked by dimensional crossover as the coupling between one-dimensional systems is increased or temperature decreased, i.e., the Q1D system goes from appearing largely 1D to largely 3D. Phase transitions occurring along the crossover can strongly enhance this effect. Understanding these crossovers and associated phase transitions can be challenging due to the very different elementary excitations of 1D systems compared to higher-dimensional ones. In the present work, we combine numerical matrix product state (MPS) methods with mean-field (MF) theory to study paradigmatic cases of dimensional crossovers and the associated phase transitions in systems of both hard-core and soft-core lattice bosons, with relevance to both condensed matter physics and ultracold atomic gases. We show that the superfluid-to-insulator transition is a first order one, as opposed to the isotropic cases and calculate transition temperatures for the superfluid states, finding excellent agreement with analytical theory. At the same time, our MPS+MF approach keeps functioning well where the current analytical framework cannot be applied. We further confirm the qualitative and quantitative reliability of our approach by comparison to exact quantum Monte Carlo calculations for the full 3D arrays.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"103 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88954858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-11-24DOI: 10.1103/PHYSREVB.103.075121
G. A. Starkov, K. Efetov
We propose a class of models exhibiting instanton crystal phase. In this phase, the minimum of the free energy corresponds to a configuration with an imaginary-time-dependent order parameter in a form of a chain of alternating instantons and antiinstantons. The resulting characteristic feature of this state is that the average of the order parameter over the imaginary time vanishes. In order to study the model in a broad region of parameters of the model quantitatively, and prove the existence of the instanton crystal phase, we develop an efficient numerical scheme, suitable for the exact treatment of the proposed models. In a certain limit, results demonstrating the existence of the instanton crystal phase are obtained also analytically. The numerical study of the model shows that there is a phase transition between the instanton crystal and the state with the imaginary-time-independent order parameter.
{"title":"Phase transition into an instanton crystal state","authors":"G. A. Starkov, K. Efetov","doi":"10.1103/PHYSREVB.103.075121","DOIUrl":"https://doi.org/10.1103/PHYSREVB.103.075121","url":null,"abstract":"We propose a class of models exhibiting instanton crystal phase. In this phase, the minimum of the free energy corresponds to a configuration with an imaginary-time-dependent order parameter in a form of a chain of alternating instantons and antiinstantons. The resulting characteristic feature of this state is that the average of the order parameter over the imaginary time vanishes. In order to study the model in a broad region of parameters of the model quantitatively, and prove the existence of the instanton crystal phase, we develop an efficient numerical scheme, suitable for the exact treatment of the proposed models. In a certain limit, results demonstrating the existence of the instanton crystal phase are obtained also analytically. The numerical study of the model shows that there is a phase transition between the instanton crystal and the state with the imaginary-time-independent order parameter.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73238073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-11-23DOI: 10.1103/PhysRevB.102.220405
R. Schick, T. Ziman, M. Zhitomirsky
In frustrated magnetic systems with competing interactions fluctuations can lift the residual accidental degeneracy. We argue that the state selection may have different outcomes for quantum and thermal order by disorder. As an example, we consider the semiclassical Heisenberg fcc antiferromagnet with only the nearest-neighbor interactions. Zero-point oscillations select the type 3 collinear antiferromagnetic state at T=0. Thermal fluctuations favor instead the type 1 antiferromagnetic structure. The opposite tendencies result in a finite-temperature transition between the two collinear states. Competition between effects of quantum and thermal order by disorder is a general phenomenon and is also realized in the J1-J2 square-lattice antiferromagnet at the critical point J2 = 0.5 J1.
{"title":"Quantum versus thermal fluctuations in the fcc antiferromagnet: Alternative routes to order by disorder","authors":"R. Schick, T. Ziman, M. Zhitomirsky","doi":"10.1103/PhysRevB.102.220405","DOIUrl":"https://doi.org/10.1103/PhysRevB.102.220405","url":null,"abstract":"In frustrated magnetic systems with competing interactions fluctuations can lift the residual accidental degeneracy. We argue that the state selection may have different outcomes for quantum and thermal order by disorder. As an example, we consider the semiclassical Heisenberg fcc antiferromagnet with only the nearest-neighbor interactions. Zero-point oscillations select the type 3 collinear antiferromagnetic state at T=0. Thermal fluctuations favor instead the type 1 antiferromagnetic structure. The opposite tendencies result in a finite-temperature transition between the two collinear states. Competition between effects of quantum and thermal order by disorder is a general phenomenon and is also realized in the J1-J2 square-lattice antiferromagnet at the critical point J2 = 0.5 J1.","PeriodicalId":8511,"journal":{"name":"arXiv: Strongly Correlated Electrons","volume":"39 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82819321","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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