arXiv subjects

Hridis K. Pal

Publications and source records attributed to Hridis K. Pal.

24 records · Page 2Linked to original sources

arXiv2017

Quantum Oscillations from Fermi Sea

Quantum oscillations are conventionally understood to arise from the Fermi level; hence, they are considered to be a proof of the existence of an underlying Fermi surface. In this article, we show that in certain situations quantum oscillations can also arise from inside the Fermi sea. We establish this analytically, supporting it with numerical calculations. Possible scenarios where such unusual behavior can occur are pointed out. In particular, in strongly particle-hole asymmetric insulators, models of which have been recently used in the context of the topological Kondo insulator SmB$_6$, we show that the oscillations arise from inside the filled band, and are not related to the gap.

cond-mat.mes-hall↗

arXiv2016

Tetrahedral Bonding in Twisted Bilayer Graphene by Carbon Intercalation

Based on ab initio calculations, we study the effect of intercalating twisted bilayer graphene with carbon. Surprisingly, we find that the intercalant pulls the atoms in the two layers closer together locally when placed in certain regions in between the layers, and the process is energetically favorable as well. This arises because in these regions of the supercell, the local environment allows the intercalant to form tetrahedral bonding with nearest atoms in the layers. Intercalating AB- or AA-bilayer graphene with carbon does not produce this effect; therefore, the nontrivial effect owes its origin to both using carbon as an intercalant and using twisted bilayer graphene as the host. This opens new routes to manipulating bilayer and multilayer van der Waals heterostructures and tuning their properties in an unconventional way.

cond-mat.mtrl-sci↗

arXiv2016

Chemical potential asymmetry and quantum oscillations in insulators

We present a theory of quantum oscillations in insulators that are particle-hole symmetric and non-topological but with arbitrary band dispersion, at both zero and non-zero temperature. At temperatures $T$ less than or comparable to the gap, the dependence of oscillations on $T$ is markedly different from that in metals and depends crucially on the position of the chemical potential $μ$ in the gap. If $μ$ is in the middle of the gap, oscillations do not change with $T$; however, if $μ$ is asymmetrically positioned in the gap, surprisingly, oscillations go to zero at a critical value of the inverse field determined by $T$ and $μ$ and then change their phase by $π$ and grow again. Additionally, the temperature dependence is different for quantities derived from the grand canonical potential, such as magnetization and susceptibility, and those derived from the density of states, such as resistivity. However, the non-trivial features arising from asymmetric $μ$ are present in both.

cond-mat.mes-hall↗

arXiv2015

Prediction of switchable half semiconductor in d$^{1}$ transition metal dichalcogenide monolayers

We propose that a half semiconducting state can exist in trigonal-prismatic transition metal dichalcogenide (TMDC) monolayers of d$^{1}$ configuration. In that state both electrons and holes are spin polarized and share the same spin channel. On the basis of hybrid density functional theory, we predict in particular that VS$_2$ monolayers are half semiconductors with a direct band gap. Moreover, we find that the conduction electron spin orientation of VS$_2$ switches under moderate strain. Our predictions thus open up intriguing possibilities for applications of VS$_2$ in spintronics and optoelectronics. Our analysis of trigonal-prismatic group-V MX$_2$ (M=V, Nb, Ta; X=S, Se, Te) monolayers reveals a broad diversity of electronic states that can be understood qualitatively in terms of localization of $d$ electrons.

cond-mat.str-el↗

arXiv2014

Theory of Twisted Bilayer Graphene Near Commensuration

Incommensurately twisted graphene bilayers are described by long-wavelength theories, but to date such theories exist only at small angles of interlayer rotation. We construct a long wavelength theory without such a restriction, instead requiring nearness to commensuration. The theory inherits its energy scale from the exactly commensurate bilayer that it is close to. It is a spatial interpolation between the low-energy theories of commensurate structures with the two possible sublattice exchange (SE) symmetries: SE even and SE odd. In addition to generalizing existing theories, our theory brings into experimental reach so far elusive commensuration physics in graphene such as band gaps and nontrivial band topology.

cond-mat.mes-hall↗

arXiv2013

Linear magnetoresistance from Dirac-like fermions in graphite

We show that magnetoresistance of Bernal-stacked graphite (with the magnetic field ${\bf B}$ parallel to the c-axis and the current in the ab plane) scales linearly with the magnetic field over an interval of classically weak fields. The linearity is related to the presence of extremely light, Dirac-like carriers near the $H$ ($H^{\prime}$)- points of the Brillouin zone. The Hall resistivity in this interval also shows a non-analytic, $B\ln |B|$ behavior, and is dominated by holes.

cond-mat.mes-hall↗