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Register a new userTemperature-field phase diagram of extreme magnetoresistance in lanthanum monopnictides
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The recent discovery of extreme magnetoresistance in LaSb introduced lanthanum monopnictides as a new platform to study topological semimetals (TSMs). In this work we report the discovery of extreme magnetoresistance in LaBi, confirming lanthanum monopnictides as a promising family of TSMs. These binary compounds with the simple rock-salt structure are ideal model systems to search for the origin of extreme magnetoresistance. Through a comparative study of magnetotransport effects in LaBi and LaSb, we construct a triangular temperature-field phase diagram that illustrates how a magnetic field tunes the electronic behavior in these materials. We show that the triangular phase diagram can be generalized to other topological semimetals with different crystal structures and different chemical compositions. By comparing our experimental results to band structure calculations, we suggest that extreme magnetoresistance in LaBi and LaSb originates from a particular orbital texture on their qasi-2D Fermi surfaces. The orbital texture, driven by spin-orbit coupling, is likely to be a generic feature of various topological semimetals.
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The acute sensitivity of the electrical resistance of certain systems to magnetic fields known as extreme magnetoresistance (XMR) has recently been explored in a new materials context with topological semimetals. Exemplified by WTe$_{2}$ and rare earth monopnictide La(Sb,Bi), these systems tend to be non-magnetic, nearly compensated semimetals and represent a platform for large magnetoresistance driven by intrinsic electronic structure. Here we explore electronic transport in magnetic members of the latter family of semimetals and find that XMR is strongly modulated by magnetic order. In particular, CeSb exhibits XMR in excess of $1.6 times 10^{6}$ % at fields of 9 T while the magnetoresistance itself is non-monotonic across the various magnetic phases and shows a transition from negative magnetoresistance to XMR with field above magnetic ordering temperature $T_{N}$. The magnitude of the XMR is larger than in other rare earth monopnictides including the non-magnetic members and follows an non-saturating power law to fields above 30 T. We show that the overall response can be understood as the modulation of conductivity by the Ce orbital state and for intermediate temperatures can be characterized by an effective medium model. Comparison to the orbitally quenched compound GdBi supports the correlation of XMR with the onset of magnetic ordering and compensation and highlights the unique combination of orbital inversion and type-I magnetic ordering in CeSb in determining its large response. These findings suggest a paradigm for magneto-orbital control of XMR and are relevant to the understanding of rare earth-based correlated topological materials.
The family of binary Lanthanum monopnictides, LaBi and LaSb, have attracted a great deal of attention as they display an unusual extreme magnetoresistance (XMR) that is not well understood. Two classes of explanations have been raised for this: the presence of non-trivial topology, and the compensation between electron and hole densities. Here, by synthesizing a new member of the family, LaAs, and performing transport measurements, Angle Resolved Photoemission Spectroscopy (ARPES), and Density Functional Theory (DFT) calculations, we show that (a) LaAs retains all qualitative features characteristic of the XMR effect but with a siginificant reduction in magnitude compared to LaSb and LaBi, (b) the absence of a band inversion or a Dirac cone in LaAs indicates that topology is insignificant to XMR, (c) the equal number of electron and hole carriers indicates that compensation is necessary for XMR but does not explain its magnitude, and (d) the ratio of electron and hole mobilities is much different in LaAs compared to LaSb and LaBi. We argue that the compensation is responsible for the XMR profile and the mobility mismatch constrains the magnitude of XMR.
We use bulk-sensitive soft X-ray angle-resolved photoemission spectroscopy and investigate bulk electronic structures of Ce monopnictides (CeX; X=P, As, Sb and Bi). By exploiting a paradigmatic study of the band structures as a function of their spin-orbit coupling (SOC), we draw the topological phase diagram of CeX and unambiguously reveal the topological phase transition from a trivial to a nontrivial regime in going from CeP to CeBi induced by the band inversion. The underlying mechanism of the topological phase transition is elucidated in terms of SOC in concert with their semimetallic band structures. Our comprehensive observations provide a new insight into the band topology hidden in the bulk of solid states.
The complexity of strongly correlated electron physics in vanadium dioxide is exemplified as its rich phase diagrams of all kinds, which in turn shed light on the mechanisms behind its various phase transitions. In this work, we map out the hydrostatic pressure - temperature phase diagram of vanadium dioxide nanobeams by independently varying pressure and temperature with a diamond anvil cell. In addition to the well-known insulating M1 (monoclinic) and metallic R (tetragonal) phases, the diagram identifies the existence at high pressures of the insulating M1 (monoclinic, more conductive than M1) phase, and two metallic phases of X (monoclinic) and O (orthorhombic, at high temperature only). Systematic optical and electrical measurements combined with density functional calculations allow us to delineate their phase boundaries as well as reveal some basic features of the transitions.
The phase diagram of Zn has been explored up to 140 GPa and 6000 K, by combining optical observations, x-ray diffraction, and ab-initio calculations. In the pressure range covered by this study, Zn is found to retain a hexagonal close-packed crystal symmetry up to the melting temperature. The known decrease of the axial ratio of the hcp phase of Zn under compression is observed in x-ray diffraction experiments from 300 K up to the melting temperature. The pressure at which the axial ratio reaches the square root of 3 value, around 10 GPa, is slightly affected by temperature. When this axial ratio is reached, we observed that single crystals of Zn, formed at high temperature, break into multiple polycrystals. In addition, a noticeable change in the pressure dependence of the axial ratio takes place at the same pressure. Both phenomena could be caused by an isomorphic second-order phase transition induced by pressure in Zn. The reported melt curve extends previous results from 24 to 135 GPa. The pressure dependence obtained for the melting temperature is accurately described up to 135 GPa by using a Simon-Glatzel equation. The determined melt curve agrees with previous low-pressure studies and with shock-wave experiments, with a melting temperature of 5060 K at 135 GPa. Finally, a thermal equation of state is reported, which at room-temperature agrees with the literature.
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