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Publications

Three-dimensional character of the Fermi surface in ultrathin LaTiO3/SrTiO3 heterostructures

Cornell Affiliated Author(s)
Author
M. Veit
M. Chan
B. Ramshaw
R. Arras
R. Pentcheva
Y. Suzuki
Abstract

LaTiO3 films on SrTiO3 single crystal substrates exhibit metallic behavior attributed to the LaTiO3 film, the interface as well as part of the SrTiO3. In the limit of ultrathin LaTiO3 films on SrTiO3, the contribution to the metallicity from strain-induced electronic structure modification of the LaTiO3 film is minimized so that the dominant contribution to metallicity is from the interface and part of the SrTiO3 due to charge transfer of 3d electrons from LaTiO3 to SrTiO3.

Journal
Physical Review B
Date Published
Funding Source
DMR-1157490

Thermodynamic Signatures of Weyl Fermions in NbP

Cornell Affiliated Author(s)
Author
K. Modic
Tobias Meng
Filip Ronning
Eric Bauer
Philip Moll
B. Ramshaw
Abstract

We present a high magnetic field study of NbP—a member of the monopnictide Weyl semimetal (WSM) family. While the monoarsenides (NbAs and TaAs) have topologically distinct left and right-handed Weyl fermi surfaces, NbP is argued to be “topologically trivial†due to the fact that all pairs of Weyl nodes are encompassed by a single Fermi surface. We use torque magnetometry to measure the magnetic response of NbP up to 60 tesla and uncover a Berry paramagnetic response, characteristic of the topological Weyl nodes, across the entire field range.

Journal
Scientific Reports
Date Published
Funding Source
1752784
715730
Group (Lab)
Brad Ramshaw Group

Magnetoresistance Scaling Reveals Symmetries of the Strongly Correlated Dynamics in BaFe2 (As1-x Px)2

Cornell Affiliated Author(s)
Author
Ian Hayes
Zeyu Hao
Nikola Maksimovic
Sylvia Lewin
Mun Chan
Ross McDonald
B. J. Ramshaw
Joel Moore
James Analytis
Abstract

The phenomenon of T-linear resistivity commonly observed in a number of strange metals has been widely seen as evidence for the breakdown of the quasiparticle picture of metals. This study shows that a recently discovered H/T scaling relationship in the magnetoresistance of the strange metal BaFe2(As1-xPx)2 is independent of the relative orientations of current and magnetic field. Rather, its magnitude and form depend only on the orientation of the magnetic field with respect to a single crystallographic axis: the direction perpendicular to the magnetic iron layers.

Journal
Physical Review Letters
Date Published
Funding Source
1106400
1157490
DGE 1106400
Group (Lab)
Brad Ramshaw Group

Chiral spin order in some purported Kitaev spin-liquid compounds

Cornell Affiliated Author(s)
Author
K.A. Modic
B.J. Ramshaw
A. Shekhter
C.M. Varma
Abstract

We examine recent magnetic torque measurements in two compounds, γ-Li2IrO3 and RuCl3, which have been discussed as possible realizations of the Kitaev model. The analysis of the reported discontinuity in torque, as an external magnetic field is rotated across the c axis in both crystals, suggests that they have a translationally invariant chiral spin order of the form (Si·Sj×Sk)≠0 in the ground state and persisting over a very wide range of magnetic field and temperature.

Journal
Physical Review B
Date Published
Group (Lab)
Brad Ramshaw Group

Resonant torsion magnetometry in anisotropic quantum materials

Cornell Affiliated Author(s)
Author
K. Modic
Maja Bachmann
B. Ramshaw
Frank Arnold
K. Shirer
Amelia Estry
Jon Betts
Nirmal Ghimire
E. Bauer
Marcus Schmidt
Michael Baenitz
E. Svanidze
Ross McDonald
Arkady Shekhter
Philip Moll
Abstract

Unusual behavior in quantum materials commonly arises from their effective low-dimensional physics, reflecting the underlying anisotropy in the spin and charge degrees of freedom. Here we introduce the magnetotropic coefficient k = ∂2F/∂θ2, the second derivative of the free energy F with respect to the magnetic field orientation θ in the crystal. We show that the magnetotropic coefficient can be quantitatively determined from a shift in the resonant frequency of a commercially available atomic force microscopy cantilever under magnetic field.

Journal
Nature Communications
Date Published
Funding Source
1157490
DMR-1157490
DMR-1644779
Group (Lab)
Brad Ramshaw Group

Scale-invariant magnetoresistance in a cuprate superconductor

Cornell Affiliated Author(s)
Author
P. Giraldo-Gallo
J. Galvis
Z. Stegen
K. Modic
Fedor Balakirev
Jon Betts
X. Lian
C. Moir
S. Riggs
J. Wu
A. Bollinger
X. He
I. Božović
B. Ramshaw
R. McDonald
G.S. Boebinger
A. Shekhter
Abstract

The anomalous metallic state in the high-temperature superconducting cuprates is masked by superconductivity near a quantum critical point. Applying high magnetic fields to suppress superconductivity has enabled detailed studies of the normal state, yet the direct effect of strong magnetic fields on the metallic state is poorly understood. We report the high-field magnetoresistance of thin-film La2–xSrxCuO4 cuprate in the vicinity of the critical doping, 0.161 ≤ p ≤ 0.190.

Journal
Science
Date Published
Funding Source
1066293
1157490
DMR-1157490
Group (Lab)
Brad Ramshaw Group

Quantum limit transport and destruction of the Weyl nodes in TaAs

Cornell Affiliated Author(s)
Author
B. Ramshaw
K. Modic
Arkady Shekhter
Yi Zhang
Eun-Ah Kim
Philip Moll
Maja Bachmann
M. Chan
Jon Betts
Fedor Balakirev
A. Migliori
N. Ghimire
E. Bauer
F. Ronning
R. McDonald
Abstract

Weyl fermions are a recently discovered ingredient for correlated states of electronic matter. A key difficulty has been that real materials also contain non-Weyl quasiparticles, and disentangling the experimental signatures has proven challenging. Here we use magnetic fields up to 95 T to drive the Weyl semimetal TaAs far into its quantum limit, where only the purely chiral 0th Landau levels of the Weyl fermions are occupied.

Journal
Nature Communications
Date Published
Funding Source
DR20160085
DMR-1308089
LDRD 20160616ECR
1157490
1308089
715730
Group (Lab)
Brad Ramshaw Group

Nonzero Berry phase in quantum oscillations from giant Rashba-type spin splitting in LaTiO3/SrTiO3 heterostructures

Cornell Affiliated Author(s)
Author
M. Veit
R. Arras
B. Ramshaw
R. Pentcheva
Y. Suzuki
Abstract

The manipulation of the spin degrees of freedom in a solid has been of fundamental and technological interest recently for developing high-speed, low-power computational devices. There has been much work focused on developing highly spin-polarized materials and understanding their behavior when incorporated into so-called spintronic devices. These devices usually require spin splitting with magnetic fields. However, there is another promising strategy to achieve spin splitting using spatial symmetry breaking without the use of a magnetic field, known as Rashba-type splitting.

Journal
Nature Communications
Date Published
Funding Source
G03
SFB/TRR 80
1157490
Group (Lab)
Brad Ramshaw Group

Pseudogap temperature T∗ of cuprate superconductors from the Nernst effect

Cornell Affiliated Author(s)
Author
Olivier Cyr-Choinière
R. Daou
Francis Laliberté
C. Collignon
S. Badoux
D. LeBoeuf
J. Chang
B. Ramshaw
D. Bonn
W. Hardy
R. Liang
J.-Q. Yan
J.-G. Cheng
J.-S. Zhou
J. Goodenough
S. Pyon
T. Takayama
H. Takagi
N. Doiron-Leyraud
Louis Taillefer
Abstract

We use the Nernst effect to delineate the boundary of the pseudogap phase in the temperature-doping phase diagram of hole-doped cuprate superconductors. New data for the Nernst coefficient ν(T) of YBa2Cu3Oy (YBCO), La1.8-xEu0.2SrxCuO4 (Eu-LSCO), and La1.6-xNd0.4SrxCuO4 (Nd-LSCO) are presented and compared with previously published data on YBCO, Eu-LSCO, Nd-LSCO, and La2-xSrxCuO4 (LSCO).

Journal
Physical Review B
Date Published
Group (Lab)
Brad Ramshaw Group

Erratum: Broken rotational symmetry on the Fermi surface of a high-Tc superconductor (npj Quantum Materials (2017) DOI: 10.1038/s41535-017-0013-z)

Cornell Affiliated Author(s)
Author
B.J. Ramshaw
N. Harrison
S.E. Sebastian
S. Ghannadzadeh
K.A. Modic
D.A. Bonn
W.N. Hardy
R. Liang
P.A. Goddard
Abstract

The original version of this Article contained the following errors in the legend of Figure 3, where: "The right hand panels are projections of this surface into the ka-kb plane," Now reads: "b-e are projections of this surface into the ka-kb plane," In addition, "The upper two panels involve two anisotropic CDWs, with Q2 = (δ,0,1/2)" Now reads: "The upper two panels involve two anisotropic CDWs, with Q1 = (δ,0,1/2) In addition, "followed by uni-axial CDW reconstruction with Q2 = (δ,0,0)," Now reads: "followed by uni-axial CDW reconstruction with Q = (δ,0,0)," In addition, "The simplest

Journal
npj Quantum Materials
Date Published
Group (Lab)
Brad Ramshaw Group