Journal of Physics: Condensed Matter最新文献

Magnetic topological semimetals are manifestations of the interplay between electronic and magnetic phases of matter, leading to peculiar characteristics such as the anomalous Hall effect (AHE) and the topological Hall effect (THE). Mn₃Sn is a time-reversal symmetry-broken magnetic Weyl semimetal showing topological characteristics within the Kagome lattice network. This study reveals a large THE in Mn_2.8Sn (6% Mn deficit Mn₃Sn) at room temperature in thexy-plane, despite being an antiferromagnet. We argue that the magnetocrystalline anisotropy induced noncoplanar spin structure is responsible for the observed THE in these systems. Further, the topological properties of these systems are highly anisotropic, as we observe a large AHE in thezx-plane. We find that Fe doping at the Mn site, Mn3-xFe_xSn (x= 0.2, 0.25, & 0.35), tunes the topological properties of these systems. These findings promise the realization of potential topotronic applications at room temperature.

The evolution of the structural, magnetic and transport properties of the intermediate compounds Nd2-xSr_xCoIrO₆withx= 0.2, 0.4, 0.6, 1 and 1.5 have been studied to establish important roles of sizes and oxidation states of cations on various phases. The replacement of Nd³⁺by Sr²⁺primarily influences the oxidation states of Co (Co²⁺→Co³⁺) and Ir (Ir⁴⁺→Ir⁵⁺) ions to maintain the charge neutrality in the entire system. The Sr dopants give rise to an increasing Co/Ir antisite disorder (ASD) to accommodate the variation of charge state and ionic radius of Co and Ir. The nature of magnetic interaction induced by Sr changes from being a ferrimagnetic (FIM) to a more dominant antiferromagnetic. The suppression of the second magnetic transition below 30 K in samples forx>0.2 is entirely due to dilution of the Nd-Nd magnetic interaction. The combined effects of ASD and mixed oxidation state of Co and Ir ions generate various types of magnetic exchange pathways and create competitive magnetic interactions to stabilize a particular magnetic ground state. In the middle compound NdSrCoIrO₆, a Griffith like phase in the temperature region 65-150 K and exchange bias field of 658 Oe at 2.3 K under a cooling field of 50 kOe has been observed. The compounds show an insulating kind of behaviour, and with hole doping the value of room temperature resistivity drastically decreases. The nature of conduction is found to follow three dimensional Mott's variable range hopping process.

Experimental determination of the structure of the superconducting order parameter in the kagome lattice compound CsV₃Sb₅is an essential step towards understanding the nature of the superconducting pairing in this material. Here we report measurements of the temperature dependence of the in-plane magnetic penetration depth,λ(T), in crystals of CsV₃Sb₅down to∼60mK. We find thatλ(T)is consistent with a fully-gapped state but with significant gap anisotropy. The magnitude of the gap minima are in the range∼0.2-0.3 Tcfor the measured samples, markedly smaller than previous estimates. We discuss different forms of potential anisotropy and how these can be linked to the V and Sb Fermi surface sheets. We highlight a significant discrepancy between the calculated and measured values ofλ(T=0)which we suggest is caused by spatially suppressed superconductivity.

Investigating two-dimensional (2D) valleytronic materials opens a new chapter in physics and facilitates the emergence of pioneering technologies. Nevertheless, this nascent field faces substantial challenges, primarily attributed to the inherent issue of valley energy degeneracy and the manipulation of valley properties. To break these constraints, the application of external fields has become pivotal for both generating and manipulating the valley properties of 2D systems. This paper takes a close look at the latest progress in modulating the valley properties of 2D valleytronic materials using external fields, covering a wide array of configurations from monolayers and bilayers to intricate heterostructures. We hope that this overview will inspire more exciting discoveries and significantly propel the evolution of valleytronics within the realm of 2D material research.

The Mott insulator Ca₂RuO₄is a paradigmatic example among transition metal oxides, where the interplay of charge, spin, orbital, and lattice degrees of freedom leads to competing quantum phases. In this paper, we focus on and review some key aspects, from the underlying physical framework and its basic properties, to recent theoretical efforts that aim to trigger unconventional quantum ground states, using several external parameters and stimuli. Using first-principle calculations, we demonstrate that Ca₂RuO₄shows a spin splitting in the reciprocal space, and identify it as an altermagnetic candidate material. The non relativistic spin-splitting has an orbital selective nature, dictated by the local crystallographic symmetry. Next, we consider two routes that may trigger exotic quantum states. The first one corresponds to transition metal substitution of the 4d⁴Ru with isovalent 3d³ions. This substitutional doping may alter the spin-orbital correlations favoring the emergence of negative thermal expansion. The second route explores fledgling states arising in a non-equilibrium steady state under the influence of an applied electric field. We show that the electric field can directly affect the orbital density, eventually leading to strong orbital fluctuations and the suppression of orbital imbalance, which may, in turn, reduce antiferromagnetism. These aspects suggest possible practical applications, as its unique properties may open up possibilities for augmenting existing technologies, surpassing the limitations of conventional materials.

The transition metal chalcogenide Cr₂S_3-xhas unique properties, such as a lower antiferromagnetic transition temperature, semiconducting behavior, and thermoelectric properties. We focus on the effects of high pressure on the properties of electrical transport and structure in the single crystal Cr₂S_2.88. It is observed that the resistance drops abruptly by approximately two orders of magnitude and the temperature derivative of the resistance changes from negative to positive after 15.7 GPa. The Cr₂S_2.88crystal has undergone transitions from a semiconductor-like phase to a metal I phase and then to another metal II phase. Simultaneously, a structural phase transition after 16.1 GPa is confirmed by synchrotron angle dispersive x-ray diffraction. After the structural phase transition, the negative magnetoresistance becomes positive with increasing pressure and shows a linear relationship in the metal II phase. Electron-type carriers dominate in the semiconductor-like phase, but hole-type carriers dominate after the structural phase transition. Our work provides an example of the effective modulation of semiconductor-like properties by pressure, which is meaningful for the innovation and development of semiconductor technology.

This study investigates quantum information scrambling (QIS) in a semiconductor quantum dot array. Starting with the 1D Transverse Field Ising model, we expand to more relevant quasi-2D frameworks such as the Heisenberg chain, super-extended Fermi-Hubbard (FH) and hardcore FH models. Assessing their relevance to semiconductor spin-qubit quantum computers, simulations of multipartite correlation formation examine qubit encoding strategies' fidelity, stability, and robustness, revealing trade-offs among these aspects. Furthermore, we investigate the weakly coupled metallic injector/detector (I/D) leads' significant impact on QIS behavior by employing multi-leadN-single orbital impurities weakly coupled Anderson models and studying the unitary evolution of the system. We observe sign flips in spatiotemporal tripartite mutual information which result in significant effects on dynamical correlation structures and their formation. Exploring carrier number effects, we identify optimal regions for QIS enhancement. Our findings emphasize the necessity of proper qubit encoding and I/D leads' influence on quantum information dynamics.

Realizing novel two-dimensional (2D) magnetic states would accelerate the development of advanced spintronic devices and the understandings of 2D magnetic physics. In this paper, we have examined the magnetic and electronic properties of 20 dynamically stable and exfoliable M₂X₂O (M = Ti-Ni; X = S-Te; excluding Co₂Te₂O). It has been unveiled that [X₄O₂]-D_2hand [M₄]-D_4hcrystal fields govern the M-3dorbital splittings in M₂X₂O. The splittings further lead to the antiferromagnetic (AFM) orderings in Ti₂S₂O/Fe₂S₂O/Fe₂Se₂O/M₂X₂O (M = V, Cr, Mn and Ni; X = S-Se) as well as the ferromagnetic orderings in Ti₂Se₂O/Ti₂Te₂O/Fe₂Te₂O/Co₂S₂O/Co₂Se₂O through kinetic and superexchange mechanisms. Notably, all the AFM M₂X₂O are 2D altermagnets, and Ti₂Se₂O/Ti₂Te₂O/Co₂S₂O/Co₂Se₂O are 2D half-metals. In particular, the anisotropicd-d/phoppings lead to the tunable altermagnetic splitting in Ti₂S₂O/Cr₂Te₂O, while the parity of V-3d_yzorbital contributes to the symmetry-protected altermagnetic splitting within V₂X₂O. These altermagnetic and half-metallic monolayer M₂X₂O provide promising candidates applied in low-dimensional spintronic devices. In addition, the potential 2D altermagnetic Weyl semimetal of Fe₂S₂O/Fe₂Se₂O, nodal-loop half-metal of Ti₂Se₂O and half-semi metal of Ti₂Te₂O facilitate to uncover novel low-dimensional topological physics. These theoretical results would expand the platform in particular for 2D altermagnets and nontrivial systems.

Quantum anomalous Hall effect generates dissipationless chiral conductive edge states in materials with large spin-orbit coupling and strong, intrinsic, or proximity magnetisation. The topological indexes of the energy bands are robust to smooth variations in the relevant parameters. Topological quantum phase transitions between states with different Chern numbers require the closing of the bulk bandgap:|C|=1→C=1/2corresponds to the transition from a topological insulator to a gapless state ink=0- quantum anomalous semimetal. Within the Bernevig-Hughes-Zhang (BHZ) model of 2D topological quantum well, this study identifies another type of topological phase transition induced by a magnetic field. The transitionC=±1→C=∓1occurs when the monotonic Zeeman field reaches the threshold value and thus triggers the reversal of edge modes chirality. The calculated threshold depends on the width of the conduction and valence bands and is more experimentally achievable the flatter the bands. The effect of the topological phase transition|ΔC|=2can be observed experimentally as a jump in magnetoresistance.

Electronic structure and magnetic interactions of a Tb adatom on graphene are investigated from first principles using combination of density functional theory and multiconfigurational quantum chemistry techniques including spin-orbit coupling (SOC) . We determine that the six-fold symmetry hollow site is the preferred adsorption site and investigate electronic spectrum for different adatom oxidation states including Tb³⁺, Tb²⁺, Tb¹⁺, and Tb⁰. For all charge states, the Tb4f8configuration is retained with other adatom valence electrons being distributed over5dxy,5dx2+y2, and6s/5d0single-electron orbitals. We find strong intra-site adatom exchange coupling that ensures that the5d6sspins are parallel to the4fspin. For Tb³⁺, the energy levels can be described by theJ = 6 multiplet split by the graphene crystal field (CF). For other oxidation states, the interaction of4felectrons with spin and orbital degrees of freedom of6s5delectrons in the presence of SOC results in the low-energy spectrum composed closely lying effective multiplets that are split by the graphene CF. Stable magnetic moment is predicted for Tb³⁺and Tb²⁺adatoms due to uniaxial magnetic anisotropy and effective anisotropy barrier around 440 cm^-1controlled by the temperature assisted quantum tunneling of magnetization through the third excited doublet. On the other hand, in-plane magnetic anisotropy is found for Tb¹⁺and Tb⁰adatoms. Our results indicate that the occupation of the6s5dorbitals can dramatically affect the magnetic anisotropy and magnetic moment stability of rare earth adatoms.