“Squeezing the best out of 2D materials”
Dr. YoungWook Kim
Department of Emergent Materials Science, DGIST
Nov. 1 (Fri.), 02:30 PM
E6-2. 1st fl. #1323
Abstract:
The study of two dimensional electron systems with extraordinarily low levels of disorder was for a
long time the exclusive privilege of the epitaxial thin film research community. The successful isolation
of graphene by mechanical exfoliation has, however, been truly disruptive. Furthermore, the assembly
of heterostructures consisting of several layers of different 2D materials in arbitrary order by exploiting
van der Waals forces has been a game changer in the field of low dimensional physics. It can be
generalized to the large class of strictly 2D materials and offers unprecedented parameters to play with
in order to tune electronic and other properties. It has led to a paradigm shift in the field of 2D condensed
matter physics with bright prospects.
In first part, I will introduce decent quantum Hall states in high quality graphene based heterostructures
that show novel even denominator fractional quantum Hall states in bilayer graphene [1] and monolayer
graphene [2], and also layer coherence mode in 2 degree twisted bilayer graphene. [3] In second part, I will show low temperature electronic transport study of van der Waals heterostructures
composed of a single graphene layer proximitized with α-RuCl3.[4] The latter is known to become
antiferromagnetically ordered below 10 K. Shubnikov-de Haas oscillations in the longitudinal
resistance together with Hall resistance measurements provide clear evidence for a band realignment
that is accompanied by a transfer of electrons originally occupying the graphene’s spin degenerate Dirac
cones into α-RuCl3 band states with in-plane spin polarization. Left behind are holes in two separate
Fermi pockets, only the dispersion of one of which is distorted near the Fermi energy due to spin
selective hybridization with these spin polarized α-RuCl3 band states. An unexpected damping of the
quantum oscillations as well as a zero-field resistance upturn close to the Néel temperature of α-RuCl3
suggest the onset of additional spin scattering due to spin fluctuations in the α-RuCl3. This approach
can unlock 　-RuCl3 hidden quantum states in low temperature through electrical transport.
[1] Youngwook Kim et al Nano Letters 15, 7445–7451 (2015)
[2] Youngwook Kim et al Nature Physics 15, 154-158 (2019)
[3] Youngwook Kim et al Unpublished
[4] Youngwook Kim et al Nano Letters 19, 4659-4665 (2019)