Publications

Strain is important for twisted bilayer graphene but its effect has not been studied in strain-controlled experiments. By fabricating graphene heterostructure samples on flexible substrates, we study how isotropic strain affects the (band) structure of such samples.

C. Liu, R. Tsuchikawa, J. Berg, L. Doherty, T. Fang, K. Watanabe, T. Taniguchi, Z. Wang, F. Liu, and V. V. Deshpande

To be submitted.

Tilted or warped Dirac cones result in asymmetric velocities and unequally spaced energy levels for left/right movers or +/- band isospin electrons, leading to a Vernier spectrum. We present evidence for this Vernier spectrum in Coulomb blockade measurements of ultraclean carbon nanotube quantum dots.

J. Berg*, N. Lotfizadeh*, D. Nichols, M. J. Senger, W. De Gottardi, E. D. Minot, V. V. Deshpande

Phys. Rev. B 110, 205401 (2024)

Surface acoustic waves (SAWs) on piezoelectric insulators can generate dynamic periodic potentials inside one-dimensional and two-dimensional materials. In this study, we investigate acoustoelectric charge pumping in graphene with very low electrostatic disorder.

D. M. Nichols, J. G. Berg, T. Taniguchi, K. Watanabe, P. Dhagat, V. V. Deshpande, A. Jander, E. D. Minot

J. Appl. Phys. 136, 024302 (2024)

Cover Article

We use nanoelectromechanical systems to study the intrinsic magnetism in MnBi2Te4 thin flakes via their magnetostrictive coupling. Our work demonstrates a technique to study magnetic phase transitions, magnetization and magnetoelastic properties of the magnetic topological insulator.

S. Liu, S. K. Chong, D. W. Kim, A. Vashist, R. Kumar, S. H. Lee, K. L. Wang, Z. Mao, F. Liu, V. V. Deshpande

arXiv:2206.04786 (under review)

Quantum spin Hall effect observations are far and few. We provide a tunable quantum spin Hall platform in form of hybridized 3D TIs through multiple realizations of the QSH effect in the parameter space of film thickness, magnetic field and transverse electric field.

S. K. Chong, L. Liu, K. Watanabe, T. Taniguchi, T. D. Sparks, F. Liu, and V. V. Deshpande

Nature Communications 13, 6386 (2022)

In this review article, we summarize the key findings by us and others of magneto- and quantum transport properties of 3D TIs and their related heterostructures with normal insulators, ferromagnets and superconductors.

S. K. Chong and V. V. Deshpande

Current Opinion in Solid State and Materials Science 25, 100939 (2021)

Invited Review Article

CNTs have been identified as a system to realize the electronic analog of a Sagnac interferometer—the most sensitive optical interferometer. We use suspended, ultraclean, known-chirality CNTs to study both Fabry-Perot and Sagnac electron interferences with good correspondence with theory.

N. Lotfizadeh, M. Senger, D. R. McCulley, E. D. Minot and V. V. Deshpande

Physical Review Letters 126, 216802 (2021)

See media coverage in Physics Today, March 2022, volume 75, number 3 “Long carbon nanotubes reveal subtleties of quantum mechanics”.

2D metal–organic frameworks have emerged as thermoelectric materials due to their high electrical and low thermal conductivities. This work studies the thermoelectric properties of copper benzenehexathiol (Cu-BHT).

R. Tsuchikawa, N. Lotfizadeh, N. Lahiri, S. Liu, M. Lach, C. Slam, J. Louie and V. V. Deshpande

Phys. Stat. Sol. A 217 (23), 2000437 (2020)

Cover Article

The Wigner crystal - a solid of electrons - has a characteristic decreasing electronic compressibility versus electron density. We measure two opposing trends of this signature as a function of CNT bandgap using single-electron transport measurements of ultraclean CNT quantum dots.

N. Lotfizadeh, D. R. McCulley, M. Senger, H. Fu, E. D. Minot, B. Skinner and V. V. Deshpande

Physical Review Letters 123, 197701 (2019)

Editor’s Suggestion

See news article in Physics magazine “Squeezing an Electron Crystal”.

In this work, we establish tunable capacitive coupling between the surface states of a bulk-insulating TI BiSbTeSe2 and study the effect of this coupling on QH plateaus and Landau level fan diagram via dual-gate control.

S. K. Chong, K. B. Han, T. D. Sparks and V. V. Deshpande

Physical Review Letters 123, 036804 (2019)

See media coverage in Media coverage in MRS Bulletin (Dec 16, 2019) “Thinness of 3D topological insulators detrimental to their metallic surfaces” and University of Utah media release “Limitation exposed in promising quantum computing material”.

Suspended metallic carbon nanotubes exhibit a remarkably large transport gap that can exceed 100 meV. Both experiment and theory suggest that strong electron-electron interactions play a crucial role. Using a thermally activated transport model, we estimate a transport gap of (450 meV nm)/D independent of the nanotube chiral angle, where D is the CNT diameter in nm.

M. J. Senger, D. R. McCulley, N. Lotfizadeh, V. V. Deshpande, E. D. Minot

Phys. Rev. B 97, 035445 (2018)

Editor’s Suggestion

We study the capacitively driven motion of a monolayer graphene nanomechanical resonator with low density of states and find contributions to the spring constant from both the chemical potential and electronic compressibility in the quantum Hall regime.

C. Chen*, V. V. Deshpande*, M. Koshino, S. Lee, A. Gondarenko, A.H. MacDonald, P. Kim, J. Hone

Nature Physics 12, 240 (2016)

Our experiment was described in the textbook “Principles of Thermodynamics” by J.-P. Ansermet and S. D. Brechet (Cambridge University Press, 2019) as an example of the use of thermodynamic potentials.

We report the first oscillators built using micrometre-size, atomically thin graphene nanomechanical resonators as the active element and achieve efficient audio signal transmission.

C. Chen, S. Lee, V. V. Deshpande, G.-H. Lee, M. Lekas, K. Shepard, J. Hone

Nature Nanotechnology 8, 923 (2013)

News and Views article by Philip Feng in Nature Nanotechnology 8, 897–898 (2013) “Tuning in to a graphene oscillator” and media coverage in Engadget “World’s smallest FM transmitter built with graphene” and Gizmodo “What Is This? A Radio for Ants?”.

We demonstrate fabrication and direct electrical measurement of circular SU-8 polymer-clamped chemical vapor deposition graphene drum resonators.

S. Lee , C. Chen, V. V. Deshpande, G. Lee, I. Lee, M. Lekas, A. Gondarenko, Y. Yu, K. Shepard, P. Kim, J. Hone

Applied Physics Letters 102, 153101 (2013)

Cover Article

We present an all-optical method for structure assignment of individual CNTs based on combined measurements of their Rayleigh and Raman scattered light.

S. Berciaud, V. V. Deshpande, R. Caldwell, Y. Miyauchi, C. Voisin, P. Kim, J. Hone, and T. F. Heinz

Phys. Stat. Sol.(b) 249, 2436 (2012)

Cover Article

We demonstrate direct electrical detection of graphene mechanical resonators. The device is operated as a resonant channel transistor, in which the effect of the oscillating capacitance is amplified by the transistor action of the graphene channel.

Y. Xu*, C. Chen*, V. V. Deshpande*, F. A. DiRenno, A. Gondarenko, D. B. Heinz, S. Liu, P. Kim, J. Hone

Applied Physics Letters 97, 243111 (2010)

Media coverage in Popular Science “In The Tiniest Receiver Ever, Graphene Can Directly Detect Radio Signals” and Technology Review “Engineers Build Radio Receiver Out Of Graphene”.

As part of a collection of “exotic matter” including topological insulators, spin liquids and non-Abelian states, we review recent experiments on correlated phenomena in 1D such as as spin–charge separation and the emergence of correlated-electron insulators.

V. V. Deshpande, M. Bockrath, L. I. Glazman, A. Yacoby

Nature 464, 209 (2010)

Review article in Nature Insight “Exotic Matter”.

This Perspective reports on two experiments on mechanical systems acting as electronic quantum dots that can be tuned at the level of single electrons.

J. Hone and V. V. Deshpande

Science 325, 1084 (2009)

Perspective

The spatial temperature profile of electrically heated single-walled nanotubes is obtained for the first time providing insights into the mechanism of thermal transport in carbon nanotubes.

V. V. Deshpande, S. Hsieh, A. W. Bushmaker, M. Bockrath, S. B. Cronin

Physical Review Letters 102, 105501 (2009)

Editor’s Suggestion

See writeup in Nanoscale Views Blog “This week in cond-mat February 21, 2009”.

Using single-electron transport spectroscopy, we show that an energy gap exists in nominally metallic single-walled carbon nanotubes with a magnitude of ~10 to 100 meV and a radius dependence of ~1/r, which is in good agreement with predictions for a nanotube Mott insulating state.

V. V. Deshpande, B. Chandra, R. Caldwell, D. S. Novikov, J. Hone and M. Bockrath

Science 323, 106 (2009)

News & Views article “Gap opens in metallic nanotubes”, Nature Nanotechnology 4, 147 (2009)” by C. Schonenberger.

A dilute system of electrons interacting through long-range Coulomb forces has been predicted to form a periodic solid known as a Wigner crystal. Here, using single-electron transport spectroscopy, we show that charge carriers in ultraclean semiconducting single-walled carbon nanotubes form a one-dimensional Wigner crystal.

V. V. Deshpande and M. Bockrath

Nature Physics 4, 314 (2008)

Selected in Nature Physics Fifth Anniversary Focus “Exotic Matter”

Nature Physics News and Views “Old nanotubes, new tricks”, 4, 266 (2008) by Jesper Nygaard
Nature Nanotechnology News and Views “A most unusual crystal”, 3, 186 (2008)
Nature Nanotechnology Research Highlights Nanoelectronics “Twists and turns”

We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNTs) to realize nanoelectromechanical switches.

V. V. Deshpande*, H.-Y. Chiu*, H. W. Ch. Postma, C. Miko, L. Forro, M. Bockrath

Nano Letters 6, 1092 (2006)

Science Magazine Editor’s Choice “Tubular switches”, 312, 1107 (2006)
Nature Research Highlights “Bridging the gap”, 442, 4 (2006)
Nature Nanozone News “Making and breaking the nanocircuit”, 29 June 2006.

We report thermal properties of individual multiwalled carbon nanotubes that suggest that nanotubes can readily conduct heat by ballistic phonon propagation.

H.-Y. Chiu*, V. V. Deshpande*, H. W. Ch. Postma, C. N. Lau, C. Miko, L. Forro, M. Bockrath

Physical Review Letters 95, 226101 (2005)

Media coverage by AIP Physics News Update “Digital heat flow”, 752 2, 2005.