Extremely large magnetoresistance (XMR) was recently discovered in WTe$_2$, triggering extensive research on this material regarding the XMR origin. Since WTe$_2$ is a layered compound with metal layers sandwiched between adjacent insulating chalcoge
nide layers, this material has been considered to be electronically two-dimensional (2D). Here we report two new findings on WTe$_2$: (1) WTe$_2$ is electronically 3D with a mass anisotropy as low as $2$, as revealed by the 3D scaling behavior of the resistance $R(H,theta)=R(varepsilon_theta H)$ with $varepsilon_theta =(cos^2 theta + gamma^{-2}sin^2 theta)^{1/2}$, $theta$ being the magnetic field angle with respect to c-axis of the crystal and $gamma$ being the mass anisotropy; (2) the mass anisotropy $gamma$ varies with temperature and follows the magnetoresistance behavior of the Fermi liquid state. Our results not only provide a general scaling approach for the anisotropic magnetoresistance but also are crucial for correctly understanding the electronic properties of WTe$_2$, including the origin of the remarkable turn-on behavior in the resistance versus temperature curve, which has been widely observed in many materials and assumed to be a metal-insulator transition.
The fidelity susceptibility is a general purpose probe of phase transitions. With its origin in quantum information and in the differential geometry perspective of quantum states, the fidelity susceptibility can indicate the presence of a phase trans
ition without prior knowledge of the local order parameter, as well as reveal the universal properties of a critical point. The wide applicability of the fidelity susceptibility to quantum many-body systems is, however, hindered by the limited computational tools to evaluate it. We present a generic, efficient, and elegant approach to compute the fidelity susceptibility of correlated fermions, bosons, and quantum spin systems in a broad range of quantum Monte Carlo methods. It can be applied both to the ground-state and non-zero temperature cases. The Monte Carlo estimator has a simple yet universal form, which can be efficiently evaluated in simulations. We demonstrate the power of this approach with applications to the Bose-Hubbard model, the spin-$1/2$ XXZ model, and use it to examine the hypothetical intermediate spin-liquid phase in the Hubbard model on the honeycomb lattice.
We use the time dependent variational matrix product state (tVMPS) approach to investigate the dynamical properties of the single impurity Anderson model (SIAM). Under the Jordan-Wigner transformation, the SIAM is reformulated into two spin-1/2 XY ch
ains with local magnetic fields along the z-axis. The chains are connected by the longitudinal Ising coupling at the end points. The ground state of the model is searched variationally within the space spanned by the matrix product state (MPS). The temporal Greens functions are calculated both by the imaginary and real time evolutions, from which the spectral information can be extracted. The possibility of using the tVMPS approach as an impurity solver for the dynamical mean field theory is also addressed. Finite temperature density operator is obtained by the ancilla approach. The results are compared to those from the Lanczos and the Hirsch-Fye quantum Monte-Carlo methods.
We carry out textit{ab initio} study of ground state phase diagram of spin-1/2 cold fermionic atoms within two-fold degenerate $p$-band of an anisotropic optical lattice. Using the Gutzwiller variational approach, we show that a robust ferromagnetic
phase exists for a vast range of band fillings and interacting strengths. The ground state crosses over from spin density wave state to spin-1 Neel state at half filling. Additional harmonic trap will induce spatial separation of varies phases. We also discuss several relevant observable consequences and detection methods. Experimental test of the results reported here may shed some light on the long-standing issue of itinerant ferromagnetism.
