18 research outputs found
linear resistivity from magneto-elastic scattering: application to PdCrO
An electronic solid with itinerant carriers and localized magnetic moments
represents a paradigmatic strongly correlated system. The electrical transport
properties associated with the itinerant carriers, as they scatter off these
local moments, has been scrutinized across a number of materials. Here we
analyze the transport characteristics associated with ultra-clean PdCrO --
a quasi two-dimensional material consisting of alternating layers of itinerant
Pd-electrons and Mott-insulating CrO layers -- which shows a pronounced
regime of linear resistivity over a wide-range of intermediate
temperatures. By contrasting these observations to the transport properties in
a closely related material PdCoO, where the CoO layers are
band-insulators, we can rule out the traditional electron-phonon interactions
as being responsible for this interesting regime. We propose a previously
ignored electron-magnetoelastic interaction between the Pd-electrons, the Cr
local-moments and an out-of-plane phonon as the main scattering mechanism that
leads to the significant enhancement of resistivity and a linear regime in
PdCrO at temperatures far in excess of the magnetic ordering temperature.
We suggest a number of future experiments to confirm this picture in PdCrO,
as well as other layered metallic/Mott-insulating materials.Comment: 7 pages, 3 figures. Supplementary material: 10 pages, 3 figure
h/e oscillations in interlayer transport of delafossites
Funding: This project was funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant no. 715730, MiTopMat) and also was supported by the Max Planck Society. A.P.M. and R.M. acknowledge support from the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter (EXC 2147). M.D.B., P.M., and V.S. acknowledge studentship funding from the EPSRC under grant no. EP/L015110/1. A.S. was supported by the Israel Science Foundation, the European Research Council (Project LEGOTOP), and the DFG through projectno.CRC-183. M.K. acknowledges support from the SIRIUS irradiation facility through project no. EMIR 2019 18-7099.Microstructures can be carefully designed to reveal the quantum phase of the wave-like nature of electrons in a metal. Here, we report phase-coherent oscillations of out-of-plane magnetoresistance in the layered delafossites PdCoO2 and PtCoO2 The oscillation period is equivalent to that determined by the magnetic flux quantum, h/e, threading an area defined by the atomic interlayer separation and the sample width, where h is Planck's constant and e is the charge of an electron. The phase of the electron wave function appears robust over length scales exceeding 10 micrometers and persisting up to temperatures of T > 50 kelvin. We show that the experimental signal stems from a periodic field modulation of the out-of-plane hopping. These results demonstrate extraordinary single-particle quantum coherence lengths in delafossites.PostprintPeer reviewe
Controllable suppression of the unconventional superconductivity in bulk and thin-film SrRuO via high-energy electron irradiation
In bulk Sr RuO, the strong sensitivity of the superconducting transition temperature c to nonmagnetic impurities provides robust evidence for a superconducting order parameter that changes sign around the Fermi surface. In superconducting epitaxial thin-film Sr RuO, the relationship between c and the residual resistivity 0, which in bulk samples is taken to be a proxy for the low-temperature elastic scattering rate, is far less clear. Using high-energy electron irradiation to controllably introduce point disorder into bulk single-crystal and thin-film Sr RuO, we show that c is suppressed in both systems at nearly identical rates. This suggests that part of 0 in films comes from defects that do not contribute to superconducting pairbreaking and establishes a quantitative link between the superconductivity of bulk and thin-film samples
Investigation of Planckian behavior in a high-conductivity oxide : PdCrO2
Funding: JFMV and DC are supported by faculty startup grants at Cornell University. ET and EB were supported by the European Research Council (ERC) under grant HQMAT (Grant Agreement No. 817799), the Israel-US Binational Science Foundation (BSF), and the Minerva Foundation.The layered delafossite metal PdCrO2 is a natural heterostructure ofhighly conductive Pd layers Kondo coupled to localized spins in the adjacentMott insulating CrO2 layers. At high temperatures T it has a T-linearresistivity which is not seen in the isostructural but non-magnetic PdCoO2.The strength of the Kondo coupling is known, as-grown crystals are extremelyhigh purity and the Fermi surface is both very simple and experimentally known.It is therefore an ideal material platform in which to investigate 'Planckianmetal' physics. We do this by means of controlled introduction of pointdisorder, measurement of the thermal conductivity and Lorenz ratio and studyingthe sources of its high temperature entropy. The T-linear resistivity is seento be due mainly to elastic scattering and to arise from a sum of severalscattering mechanisms. Remarkably, this sum leads to a scattering rate within10% of the Planckian value of kBT/ℏ.Publisher PDFPeer reviewe
Directional ballistic transport in the two-dimensional metal PdCoO2
This project was supported by the Max Planck Society and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (MiTopMat, grant agreement no. 715730). M.D.B. and P.H.M. acknowledge EPSRC for PhD studentship support through grant number EP/L015110/1. Research in Dresden benefits from the environment of the Excellence Cluster ct.qmat. A.S. acknowledges support from an ARCS Foundation Fellowship, a Ford Foundation Predoctoral Fellowship and a National Science Foundation Graduate Research Fellowship. A.S. would thanks Z. Gomez and E. Huang for helpful discussions and T. Devereaux for letting us use his group cluster. Computational work was performed on the Sherlock cluster at Stanford University and on resources of the National Energy Research Scientific Computing Center, supported by the DOE under contract DE_AC02-05CH11231. T.S. acknowledges support from the Emergent Phenomena in Quantum Systems initiative of the Gordon and Betty Moore Foundation, and from the Natural Sciences and Engineering Research Council of Canada (NSERC), in particular the Discovery Grant (RGPIN-2020-05842), Accelerator Supplement (RGPAS-2020-00060) and Discovery Launch Supplement (DGECR-2020-00222). T.S. contributed to this work prior to joining AWS. D.G.-G.’s and A.W.B.’s involvement in calculations was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division under contract DE-AC02-76SF00515. E.Z. and M.M. thank the International Max Planck Research School for Chemistry and Physics of Quantum Materials (IMPRS-CPQM) for financial support. G.B. and D.A.B. acknowledge support from the Natural Sciences and Engineering Research Council of Canada (NSERC Discovery Grant RGPIN-2018-04280) and from the Canada First Research Excellence Fund.In an idealized infinite crystal, the material properties are constrained by the symmetries of the unit cell. The point-group symmetry is broken by the sample shape of any finite crystal, but this is commonly unobservable in macroscopic metals. To sense the shape-induced symmetry lowering in such metals, long-lived bulk states originating from an anisotropic Fermi surface are needed. Here we show how a strongly facetted Fermi surface and the long quasiparticle mean free path present in microstructures of PdCoO2 yield an in-plane resistivity anisotropy that is forbidden by symmetry on an infinite hexagonal lattice. We fabricate bar-shaped transport devices narrower than the mean free path from single crystals using focused ion beam milling, such that the ballistic charge carriers at low temperatures frequently collide with both of the side walls that define the channel. Two symmetry-forbidden transport signatures appear: the in-plane resistivity anisotropy exceeds a factor of 2, and a transverse voltage appears in zero magnetic field. Using ballistic Monte Carlo simulations and a numerical solution of the Boltzmann equation, we identify the orientation of the narrow channel as the source of symmetry breaking.Publisher PDFPeer reviewe
Investigation of transport regimes in restricted geometries of ultra-pure natural heterostructures
This thesis describes investigations into the origins of the unconventional electrical transport of the non-magnetic delafossite metals PtCoO₂ and PdCoO₂ and the magnetic delafossite metal PdCrO₂ using focused ion beam microstructuring techniques. These compounds are among the highest conductivity materials known, with an extreme purity of up to 1 defect in 120,000 atoms. This remarkable purity, together with the hexagonal Fermi surface, opens the possibility of studying novel regimes of mesoscopic physics. This work is split into two parts. In the first part, I will review the key properties of non-magnetic delafossite metals and the application of focused ion beam microstructuring to transport measurements within low resistivity materials. The related experimental chapter describes an investigation which uses the high energy electron irradiation investigation to probe the effects of a non-circular Fermi surface on the transport within bars and four-terminal, square-shaped junctions inside the ballistic regime. The other studies were concentrated on the magnetic delafossite metal PdCrO₂. I will describe a new method of microstructure preparation which was created for PdCrO₂ transport studies but is widely applicable to other materials. This material obeys the Planckian bound at a wide range of temperatures between 200 K and 500 K. The accompanying experimental chapter details an investigation by high energy electron irradiation of the origin of this behaviour. The new method of mounting microstructures also allows, for the first time, the study of studying unconventional transport regimes in PdCrO₂
Low-symmetry nonlocal transport in microstructured squares of delafossite metals
Funding: Max Planck Society. Engineering and Physical Science Research Council PhD studentship support via grant EP/L015110/1 (PHM,MDB). Deutsche Forschungsgemeinschaft Cluster of Excellence ct.qmat EXC 2147, project-id 390858490. European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (MiTopMat - grant agreement No 715730) (PJWM,CP).Intense work studying the ballistic regime of electron transport in two-dimensional systems based on semiconductors and graphene had been thought to have established most of the key experimental facts of the field. In recent years, however, additional forms of ballistic transport have become accessible in the quasi–two-dimensional delafossite metals, whose Fermi wavelength is a factor of 100 shorter than those typically studied in the previous work and whose Fermi surfaces are nearly hexagonal in shape and therefore strongly faceted. This has some profound consequences for results obtained from the classic ballistic transport experiment of studying bend and Hall resistances in mesoscopic squares fabricated from delafossite single crystals. We observe pronounced anisotropies in bend resistances and even a Hall voltage that is strongly asymmetric in magnetic field. Although some of our observations are nonintuitive at first sight, we show that they can be understood within a nonlocal Landauer-Büttiker analysis tailored to the symmetries of the square/hexagonal geometries of our combined device/Fermi surface system. Signatures of nonlocal transport can be resolved for squares of linear dimension of nearly 100 µm, approximately a factor of 15 larger than the bulk mean free path of the crystal from which the device was fabricated.Publisher PDFPeer reviewe
Low-symmetry nonlocal transport in microstructured squares of delafossite metals
Intense work studying the ballistic regime of electron transport in two-dimensional systems based on semiconductors and graphene had been thought to have established most of the key experimental facts of the field. In recent years, however, additional forms of ballistic transport have become accessible in the quasi-two-dimensional delafossite metals, whose Fermi wavelength is a factor of 100 shorter than those typically studied in the previous work and whose Fermi surfaces are nearly hexagonal in shape and therefore strongly faceted. This has some profound consequences for results obtained from the classic ballistic transport experiment of studying bend and Hall resistances in mesoscopic squares fabricated from delafossite single crystals. We observe pronounced anisotropies in bend resistances and even a Hall voltage that is strongly asymmetric in magnetic field. Although some of our observations are nonintuitive at first sight, we show that they can be understood within a nonlocal Landauer-Buttiker analysis tailored to the symmetries of the square/hexagonal geometries of our combined device/Fermi surface system. Signatures of nonlocal transport can be resolved for squares of linear dimension of nearly 100 mu m, approximately a factor of 15 larger than the bulk mean free path of the crystal from which the device was fabricated.QMA
Vortex motion in reconfigurable three-dimensional superconducting nanoarchitectures
When materials are patterned in three dimensions, there exist opportunities
to tailor and create functionalities associated with an increase in complexity,
the breaking of symmetries, and the introduction of curvature and non-trivial
topologies. For superconducting nanostructures, the extension to the third
dimension may trigger the emergence of new physical phenomena, as well as
advances in technologies. Here, we harness three-dimensional (3D)
nanopatterning to fabricate and control the emergent properties of a 3D
superconducting nanostructure. Not only are we able to demonstrate the
existence and motion of superconducting vortices in 3D but, with simulations,
we show that the confinement leads to a well-defined bending of the vortices
within the volume of the structure. Moreover, we experimentally observe a
strong geometrical anisotropy of the critical field, through which we achieve
the reconfigurable coexistence of superconducting and normal states in our 3D
superconducting architecture, and the local definition of weak links. In this
way, we uncover an intermediate regime of nanosuperconductivity, where the
vortex state is truly three-dimensional and can be designed and manipulated by
geometrical confinement. This insight into the influence of 3D geometries on
superconducting properties offers a route to local reconfigurable control for
future computing devices, sensors, and quantum technologies.Comment: 22 pages, 12 figure