arXiv subjects

Amit

Publications and source records attributed to Amit.

6 recordsLinked to original sources

arXiv2018

A de Hass-van Alphen study of the Type-II Dirac semimetal candidates $A$Te$_2$ ($A =$ Pt, Pd)

We report on a magneto-transport and quantum oscillations study on high quality single crystals of the transition metal di-tellurides PtTe$_2$ and PdTe$_2$. The de Haas-van Alphen (dHvA) oscillations in the magnetization measurements on PtTe$_2$ reveal a complicated, anisotropic band structure characterized by low effective masses and high mobilities for the carriers. Extracted transport parameters for PtTe$_2$ reveal a strong anisotropy which could be related to the tilted nature of Dirac cone. Using a Landau level fan diagram analysis we find at least one Fermi surface orbit with a Berry phase of $\pi$ consistent with Dirac electrons for both PtTe$_2$ and PdTe$_2$. The light effective mass and high mobility are also consistent with Dirac electrons in PtTe$_2$. Our results suggest that similar to PdTe$_2$, PtTe$_2$ might also be a three dimensional Dirac semimetal.

cond-mat.mtrl-sci↗

arXiv2018

Mixed type I and type II superconductivity due to intrinsic electronic inhomogeneities in the type II Dirac semimetal PdTe2

The type II Dirac semimetal PdTe$_2$ is unique in the family of topological parent materials because it displays a superconducting ground state below 1.7 K. Despite wide speculations on the possibility of an unconventional topological superconducting phase, tunneling and heat capacity measurements revealed that the superconducting phase of PdTe$_2$ follows predictions of the microscopic theory of Bardeen, Cooper and Shriefer (BCS) for conventional superconductors. The superconducting phase in PdTe$_2$ is further interesting because it also displays properties that are characteristics of type-I superconductors and are generally unexpected for binary compounds. Here, from scanning tunneling spectroscopic measurements we show that the surface of PdTe$_2$ displays intrinsic electronic inhomegenities in the normal state which leads to a mixed type I and type II superconducting behaviour along with a spatial distribution of critical fields in the superconducting state. Understanding of the origin of such inhomogeneities may be important for understanding the topological properties of PdTe$_2$ in the normal state.

cond-mat.supr-con↗

arXiv2018

Observation of Chiral character deep in the topological insulating regime in Bi$_{1-x}$Sb$_x$

Bi$_{1-x}$Sb$_x$ is a topological insulator (TI) for $x \approx 0.03 $--$0.20$. Close to the Topological phase transition at $x = 0.03$, a magnetic field induced Weyl semi-metal (WSM) state is stabilized due to the splitting of the Dirac cone into two Weyl cones of opposite chirality. A signature of the Weyl state is the observation of a Chiral anomaly [negative longitudnal magnetoresistance (LMR)] and a violation of the Ohm's law (non-linear $I-V$). We report the unexpected discovery of a Chiral anomaly in the whole range ($x = 0.032, 0.072, 0.16$) of the TI state. This points to a field induced WSM state in an extended $x$ range and not just near the topological transition at $x = 0.03$. Surprisingly, the strongest Weyl phase is found at $x = 0.16$ with a non-saturating negative LMR much larger than observed for $x = 0.03$. The negative LMR vanishes rapidly with increasing angle between $B$ and $I$. Additionally, non-linear $I$--$V$ is found for $x = 0.16$ indicating a violation of Ohm's law. This unexpected observation of a strong Weyl state in the whole TI regime in Bi$_{1-x}$Sb$_x$ points to a gap in our understanding of the detailed electronic structure evolution in this alloy system.

cond-mat.mtrl-sci↗

arXiv2018

Heat capacity evidence for conventional superconductivity in the Type-II Dirac semi-metal PdTe$_2$

We use electrical transport, magnetoresistance, and heat capacity measurements on high quality single crystals of the recently discovered superconducting Type-II Dirac semi-metal PdTe$_2$, to probe the nature of it's superconducting phase. The magnitude of the electronic heat capacity anomaly at $T_c$, the low temperature exponential $T$ dependence of the heat capacity, and a conventional $H - T$ phase diagram establish that the superconductivity in PdTe$_2$ is conventional in nature despite the presence of a topologically non-trivial Fermi surface band which contributes to the electrical conduction.

cond-mat.supr-con↗

arXiv2017

Conventional Superconductivity in Type II Dirac Semimetal PdTe$_2$

The transition metal dichalcogenide PdTe$_2$ was recently shown to be a unique system where a type II Dirac semimetallic phase and a superconducting phase co-exist. This observation has led to wide speculation on the possibility of the emergence of an unconventional topological superconducting phase in PdTe$_2$. Here, through direct measurement of the superconducting energy gap by scanning tunneling spectroscopy (STS), and temperature and magnetic field evolution of the same, we show that the superconducting phase in PdTe$_2$ is conventional in nature. The superconducting energy gap is measured to be 326 $\mu$eV at 0.38 K and it follows a temperature dependence that is well described within the framework of Bardeen-Cooper-Schriefer's (BCS) theory of conventional superconductivity. This is surprising because our quantum oscillation measurements confirm that at least one of the bands participating in transport has topologically non-trivial character.

cond-mat.supr-con↗

arXiv2016

The H-T and P-T phase diagram of the superconducting phase in Pd:Bi$_2$Te$_3$

We study the magnetic field vs temperature ($H$--$T$) and pressure vs temperature ($P$--$T$) phase diagram of the $T_c \approx 5.5$~K superconducting phase in Pd$_x$Bi$_2$Te$_3$ ($x \approx 1$) using electrical resistivity versus temperature measurements at various applied magnetic fields ($H$) and magnetic susceptibility versus temperature measurements at various applied magnetic fields ($H$) and pressure ($P$). The $H$--$T$ phase diagram has an initial upward curvature as observed in some unconventional superconductors. The critical field extrapolated to $T = 0$~K is $H_c (0) \approx 6$--$10$~kOe. The $T_c$ is suppressed approximately linearly with pressure at a rate $dT_c/dP \approx -0.28$~K/GPa.

cond-mat.supr-con↗