Research focuses:

Exploring Novel Quantum Phenomena and Materials for Advanced Device Applications.

•  Quantum Phenomena in Low-Dimensional Materials.

• Topological Phases and Long-Range Order in Strongly Correlated Materials.

• Charge/Spin Density Wave Physics and Phase Transitions.

• Critical Phenomena in Strongly Correlated Materials.

• Utilization of Quantum Properties for Device Applications.

Research summary: 

Our research is primarily centered around investigating the intriguing quantum phenomena exhibited by low-dimensional quantum materials with a layered structures. Specifically, we are interested in studying emerging phenomena arising from the interplay of electronic state topology and collective order in vdW quantum materials. The families of (a) Quasi-2D vdW ferromagnets and topological materials, and (b) Quasi-1D vdW materials serve as an exceptional and versatile platform for probing critical quantum phenomena such as the dynamic response of charge density waves (CDW) and topological phases in 1D chains.

Quasi--1D compounds represent a fascinating class of quantum materials characterized by reduced dimensionality and enhanced electronic correlations. These systems often host a spatially modulated condensate of conduction electrons, known as a charge density wave (CDW), which is typically accompanied by periodic lattice distortions due to strong electron–phonon coupling. The collective dynamics of the CDW state exhibit rich low-energy behavior under external perturbations such as electric, optical, and magnetic fields. Notably, the nonlinear response of the ordered CDW phase gives rise to a range of emergent phenomena, including nonlinear conductivity, giant low-frequency dielectric constants (on the order of 10⁹), and broadband electrical noise under nonequilibrium conditions.

Addition to their electronic properties, quasi-1D systems incorporating localized spins display a variety of exotic magnetic behaviors. For instance, spin-½ chains are known to host gapless spin excitations consistent with Luttinger liquid theory, while spin-1 chains exhibit a finite excitation gap in accordance with the Haldane conjecture. The lack of inversion symmetry in certain quasi-1D lattices further permits higher-order interactions, such as Dzyaloshinskii–Moriya (DM) interactions, which couple the magnetic spin texture to the underlying electronic polarity. These magnetoelectric couplings can induce spin canting and stabilize unconventional magnetic configurations, including spin spirals, even in systems that are nominally centrosymmetric. 

       To explore the novel physics in quasi-1D systems, we are investigating the family of one-dimensional (1D) or quasi-1D linear-chain compounds (MX4)nI [M=Nb, Ta ; X= S, Se, Te and n=2, 3, and 10/3] and M2PdXy [M= Nb and Ta, X=S, Se, Te; y = 5, 6] in details for their wide varieties of phase transitions and phase coexistences. Typically, in the (MX4)nI group, M atoms from long 1D chains, which are surrounded by rectangular X antiprisms and stabilized by I ions between the chains. The filling of the metal dz2 band governs the electronic properties determined by n as (n − 1)/2n.  These quasi-1D materials show some unexpected phenomena, like unusual dynamic properties in optical spectroscopy and photoemission, large thermopower that changes signs at finite temperature, and incomplete phonon softening near the phase transition.

Strong correlations and competing interactions among charge, spin, orbital, and lattice degrees of freedom in quantum materials (QMs) drive a host of emergent phenomena and unconventional phase transitions. Decades of research have led to the discovery of novel QMs that underpin both technological innovation and advances in condensed matter physics.

A major recent development is the discovery of topological materials—including topological insulators and Dirac/Weyl semimetals—characterized by nontrivial band topology and strong spin-orbit coupling. These features give rise to robust, dissipationless edge or surface states and enable a range of exotic quantum effects such as:

• Chiral magnetic phenomena

• Colossal photovoltaic response

• Quantum anomalous Hall effect

• Unconventional magneto-oscillations

Our current work focuses on layered topological semimetals, particularly WTe₂ and MoTe₂, as model systems to explore low-dimensional topological transport and nonequilibrium dynamics.

The 2D magnetic materials are expected to host many scientific novel phenomena such as quantum anomalous Hall effect, long-range entanglement, and topological phase transitions. The spin-polarized conduction of electrons results in great promise for spintronics applications. Realizing high-efficiency spintronic devices based on 2D magnetic materials would tremendously impact nanoscale spintronics, data storage, and current computing platforms. However, the critical temperatures of most of these 2D magnetic systems are very low due to the limit imposed by the Mermin–Wagner theorem. 

We work on various promising candidates of 2D magnetic materials, in particular,  XI3 (X=Vi,Cr) and FenGeTe2 [Satyabrata Bera et al., PRB (2023)], employing magnetization measurements and magneto-optical spectroscopy (Raman and optical Kerr rotation) and study their fundamental magnetic properties, including Curie temperature, magnetic ground states, and domain dynamics as a function of layer number. We explore magnetic ground states and ways to enhance the critical temperature of towards room temperature 2D magnetism by escaping the limit imposed by Mermin–Wagner theorem.  

The quantum materials are engineered with precise control over their atomic and molecular structures, allowing for the manipulation of their electronic, magnetic, and optical properties. Quantum materials possess remarkable characteristics such as superconductivity, quantum confinement effects, and topological insulating behavior, which make them promising for a wide range of applications in electronics, energy storage, and quantum computing. One specific application that has gained significant attention is resistive memory, also known as memristors. These nanoscale devices utilize the inherent resistive switching behavior of certain materials to store and retrieve data. 

The nanostructures within the memristor play a crucial role in determining its performance, as they can significantly influence the switching speed, endurance, and stability of the device. As researchers delve deeper into understanding and manipulating quantum materials at the nanoscale, the potential for breakthroughs in resistive memory and other technologies continues to grow, paving the way for more efficient and advanced electronic devices.