Research Projects

Electronic correlations, electron-phonon couplings in materials often results in very surprising and sometimes very unexpected behavior. Typical examples of such interactions in condensed matter systems are the stabilization of superconductivity, charge density waves (CDW), Kondo effect, etc. Recently, quantum materials with flat bands are of strong scrutiny by the condensed matter physicists as these materials show exotic quantum behavior due to strong electron-electron interactions. A classic case is the Moire pattern in bilayer graphene - where two monolayers of graphene are stacked at a certain angle with respect to the other. The electronic interaction between the two graphene layers leads to flat band suggesting strong electron-electron correlations. In materials showing Kondo effect, the itinerant electrons interact with localized magnetic moments thereby screening the localized moments. Thus singlet states from many body systems are formed as a result of strong electron electron interactions. Traditionally, Kondo behavior was observed in f-electron (heavy fermion) systems. However, recently such behavior has been reported for d-electron systems, particularly van der Walls ferromagnets FenGeTe2, where, n = 3 and 5. A pertinent question for observation of the Kondo effect in these d-electron systems is the origin of the effect. It is clear the magnetic moment of d-electron must acquire “localized” character which has been attributed to the presence of a nearly non-dispersive band, typically observed for many f-electron systems. Due to the itinerant nature of electrons in such systems, there may be significant influence on the band structure due to the Kondo-lattice behavior. Thus, it is essential to probe the interplay between electrical and magnetic degrees of freedom in such systems. In fact, stabilization of charge order (CO) based on Kondo lattice model were already suggested by theory groups for 2- or more dimensional heavy fermion (f-electron) materials. Typically, for stabilization of CO in a system, inter site (repulsive) Coulomb interaction plays a major role. However, in Kondo lattice systems, theory suggests that the CO may stabilize due to the strong Kondo coupling between itinerant electron moments and localized moments without the need for inter site Coulomb repulsion. A recent development of observations of Kondo effect in van der Waals magnets such as Fe3GeTe2 and heterostructures of 1T/1H-TaS2 calls for an investigation of the electronic ordering in such systems. The heterostructure of van der Waals materials can be considered as "artificial materials" as materials of various different properties can be coupled with very clean interfaces to investigate new properties arising out of such coupling. Such systems also allow finding materials with tunability of physical properties. Therefore, studying the interplay of different electronic behavior such as Kondo screening and modulated charge density in charge density wave (CDW) systems is a very relevant problem and may lead to novel and emergent physics. In this proposed project we aim to explore the interplay of these two phenomenon in which electron correlation is the key interaction which governs the physics. We will fabricate "artificial samples", that is heterostructures of two van der Waals materials which independently show CDW behavior and Kondo effect. We will explore the electronic coupling between the two systems by carrying out detailed measurements of electrical transport in temperature down to 300 mK and external magnetic field (magnetotransport), Scanning Tunneling Microscopy and spectroscopy down to 330 mK and in external field and resistance fluctuation (noise) spectroscopy. We will investigate the global electrical and magnetotransport behavior and LOCAL density of states (LDOS) in details. With theoretical collaboration, who will be involved as Honorary -PI (H-PI), we aim to achieve in-depth understanding of the coupled system.