Theses Doctoral

Transport Investigations of Superconductivity in Few-Layered Td - MoTe2

Jindal, Apoorv

Achieving electrostatic control of quantum phases is at the heart of condensed matter physics allowing us to interface fundamentally different electronic orders and observe their interplay with one another. Recent investigations have revealed emergent superconductivity tuned by the electric field effect in two-dimensional (2D) semimetals and moiré heterostructures. Through electrical transport measurements, we investigate superconductivity in few-layered Td - MoTe2 in this dissertation.

Given its sensitivity to the ambient, a process to encapsulate and simultaneously electrically contact the material is developed to preserve the innate properties of MoTe2. At the outset, we observe a dramatic enhancement of superconducting critical temperature (Tc) in few-layered MoTe2. Monolayer’s Tc of ∼ 7.5 K is about 60x higher than the bulk. Reflecting its relatively small Fermi surface, superconductivity is tunable with electrostatic gating andresponse to in-plane magnetic fields reveals a tilted Ising spin texture.

Some 2D crystal systems exhibit a polar crystal structure resulting in a robust, nonvolatile and bistable interlayer polarization giving rise to electric-field tunable ferroelectricity. Remarkably, we show that noncentrosymmetric bilayer Td - MoTe2 exhibits such ferroelectric switching while simultaneously being a superconductor, two electronic orders conventionally thought to be incompatible with one another. Further, electrostatic doping unveils a superconductingdome. It is found that the maximum Tc is concomitant with compensated electron and hole carrier densities and vanishes when one of the Fermi pockets disappears with doping pointing towards a pairing mechanism mediated by Fermi surface nesting between electron and hole pockets.

Finally, in-plane magnetotransport measurements reveal a two-fold symmetric superconductivity around the crystal axes for bilayer MoTe2. Superconductivity is maximized when magnetic field is parallel to the ?-axis of the crystal and minimized for b-axis. Although unsurprising given the ?2 crystal symmetry, these results lend further credence to the tilted Ising spin texture, as unveiled from Hc2|| measurements on the monolayer.


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More About This Work

Academic Units
Thesis Advisors
Pasupathy, Abhay N.
Ph.D., Columbia University
Published Here
November 1, 2023