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Yin L, Che L, Le T, Chen Y, Zhang Y, Lee H, Gnida D, Thompson JD, Kaczorowski D, Lu X. Point-contact spectroscopy of heavy fermion superconductors Ce 2PdIn 8and Ce 3PdIn 11in comparison with CeCoIn 5. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:205603. [PMID: 33690181 DOI: 10.1088/1361-648x/abed19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Accepted: 03/09/2021] [Indexed: 06/12/2023]
Abstract
We report point-contact spectroscopy measurements on heavy fermion cousins CeCoIn5, Ce2PdIn8and Ce3PdIn11to systematically study the hybridization betweenfand conduction electrons. Below a temperatureT*, the spectrum of each compound exhibits an evolving Fano-like conductance shape, superimposed on a sloping background, that suggests the development of hybridization between localfand itinerant conduction electrons in the coherent heavy fermion state belowT*. We present a quantitative analysis of the conductance curves with a two-channel model to compare the tunneling process between normal metallic silver particles in our soft point-contact and heavy-fermion single crystals CeCoIn5, Ce2PdIn8and Ce3PdIn11.
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Affiliation(s)
- Lichang Yin
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, People's Republic of China
| | - Liqiang Che
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, People's Republic of China
| | - Tian Le
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, People's Republic of China
| | - Ye Chen
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, People's Republic of China
| | - Yongjun Zhang
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, People's Republic of China
| | - Hanoh Lee
- Department of Physics, Sungkyunkwan University, Suwon 440-746, Republic of Korea
| | - Daniel Gnida
- Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw, Poland
| | - Joe D Thompson
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States of America
| | - Dariusz Kaczorowski
- Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw, Poland
- Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okolna 2, 50-422 Wroclaw, Poland
| | - Xin Lu
- Center for Correlated Matter and Department of Physics, Zhejiang University, Hangzhou 310058, People's Republic of China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, People's Republic of China
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Yang FB. Hybridization Induced Competitive Scanning Tunneling Interference Process into a Heavy Fermion System. CHINESE PHYSICS LETTERS 2018; 35:077502. [DOI: 10.1088/0256-307x/35/7/077502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
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Abstract
The second-order phase transition into a hidden order phase in URu2Si2 goes along with an order parameter that is still a mystery, despite 30 years of research. However, it is understood that the symmetry of the order parameter must be related to the symmetry of the low-lying local electronic [Formula: see text]-states. Here, we present results of a spectroscopic technique, namely core-level nonresonant inelastic X-ray scattering (NIXS). This method allows for the measurement of local high-multipole excitations and is bulk-sensitive. The observed anisotropy of the scattering function unambiguously shows that the 5[Formula: see text] ground-state wave function is composed mainly of the [Formula: see text] with majority [Formula: see text] = [Formula: see text] + [Formula: see text] and/or [Formula: see text] singlet states. The incomplete dichroism indicates the possibility that quantum states of other irreducible representation are mixed into the ground state.
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Lee WC, Greene LH. Recent progress of probing correlated electron states by point contact spectroscopy. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2016; 79:094502. [PMID: 27533341 DOI: 10.1088/0034-4885/79/9/094502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We review recent progress in point contact spectroscopy (PCS) to extract spectroscopic information out of correlated electron materials, with the emphasis on non-superconducting states. PCS has been used to detect bosonic excitations in normal metals, where signatures (e.g. phonons) are usually less than 1% of the measured conductance. In the superconducting state, point contact Andreev reflection (PCAR) has been widely used to study properties of the superconducting gap in various superconductors. It has been well-recognized that the corresponding conductance can be accurately fitted by the Blonder-Tinkham-Klapwijk (BTK) theory in which the AR occurring near the point contact junction is modeled by three parameters; the superconducting gap, the quasiparticle scattering rate, and a dimensionless parameter, Z, describing the strength of the potential barrier at the junction. AR can be as large as 100% of the background conductance, and only arises in the case of superconductors. In the last decade, there have been more and more experimental results suggesting that the point contact conductance could reveal new features associated with the unusual single electron dynamics in non-superconducting states, shedding a new light on exploring the nature of the competing phases in correlated materials. To correctly interpret these new features, it is crucial to re-examine the modeling of the point contact junctions, the formalism used to describe the single electron dynamics particularly in point contact spectroscopy, and the physical quantity that should be computed to understand the conductance. We will summarize the theories for point contact spectroscopy developed from different approaches and highlight these conceptual differences distinguishing point contact spectroscopy from tunneling-based probes. Moreover, we will show how the Schwinger-Kadanoff-Baym-Keldysh (SKBK) formalism together with the appropriate modeling of the nano-scale point contacts randomly distributed across the junction leads to the conclusion that the point contact conductance is proportional to the effective density of states, a physical quantity that can be computed if the electron self energy is known. The experimental data on iron based superconductors and heavy fermion compounds will be analyzed in this framework. These recent developments have extended the applicability of point contact spectroscopy to correlated materials, which will help us achieve a deeper understanding of the single electron dynamics in strongly correlated systems.
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Affiliation(s)
- Wei-Cheng Lee
- Department of Physics, Applied Physics, and Astronomy, Binghamton University-State University of New York, Binghamton, NY, USA
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Yang YF. Two-fluid model for heavy electron physics. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2016; 79:074501. [PMID: 27214153 DOI: 10.1088/0034-4885/79/7/074501] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The two-fluid model is a phenomenological description of the gradual change of the itinerant and local characters of f-electrons with temperature and other tuning parameters and has been quite successful in explaining many unusual and puzzling experimental observations in heavy electron materials. We review some of these results and discuss possible implications of the two-fluid model in understanding the microscopic origin of heavy electron physics.
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Affiliation(s)
- Yi-Feng Yang
- Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China. Collaborative Innovation Center of Quantum Matter, Beijing 100190, People's Republic of China
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Tortello M, Park WK, Ascencio CO, Saraf P, Greene LH. Design and construction of a point-contact spectroscopy rig with lateral scanning capability. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:063903. [PMID: 27370466 DOI: 10.1063/1.4953340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 05/23/2016] [Indexed: 06/06/2023]
Abstract
The design and realization of a cryogenic rig for point-contact spectroscopy measurements in the needle-anvil configuration is presented. Thanks to the use of two piezoelectric nano-positioners, the tip can move along the vertical (z) and horizontal (x) direction and thus the rig is suitable to probe different regions of a sample in situ. Moreover, it can also form double point-contacts on different facets of a single crystal for achieving, e.g., an interferometer configuration for phase-sensitive measurements. For the later purpose, the sample holder can also host a Helmholtz coil for applying a small transverse magnetic field to the junction. A semi-rigid coaxial cable can be easily added for studying the behavior of Josephson junctions under microwave irradiation. The rig can be detached from the probe and thus used with different cryostats. The performance of this new probe has been tested in a Quantum Design PPMS system by conducting point-contact Andreev reflection measurements on Nb thin films over large areas as a function of temperature and magnetic field.
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Affiliation(s)
- M Tortello
- Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Torino 10129, Italy
| | - W K Park
- Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - C O Ascencio
- Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - P Saraf
- Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - L H Greene
- Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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Narasiwodeyar S, Dwyer M, Liu M, Park WK, Greene LH. Two-step fabrication technique of gold tips for use in point-contact spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2015; 86:033903. [PMID: 25832241 DOI: 10.1063/1.4913661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
For a successful point-contact spectroscopy (PCS) measurement, metallic tips of proper shape and smoothness are essential to ensure the ballistic nature of a point-contact junction. Until recently, the fabrication of Au tips suitable for use in point-contact spectroscopy has remained more of an art involving a trial and error method rather than an automated scientific process. To address these issues, we have developed a technique with which one can prepare high quality Au tips reproducibly and systematically. It involves an electronic control of the driving voltages used for an electrochemical etching of a gold wire in a HCl-glycerol mixture or a HCl solution. We find that a stopping current, below which the circuit is set to shut off, is a single very important parameter to produce an Au tip of desired shape. We present detailed descriptions for a two-step etching process for Au tips and also test results from PCS measurements using them.
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Affiliation(s)
- S Narasiwodeyar
- Department of Physics and Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - M Dwyer
- Department of Physics and Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - M Liu
- Department of Physics and Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - W K Park
- Department of Physics and Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - L H Greene
- Department of Physics and Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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Lee WC, Park WK, Arham HZ, Greene LH, Phillips P. Theory of point contact spectroscopy in correlated materials. Proc Natl Acad Sci U S A 2015; 112:651-6. [PMID: 25561532 PMCID: PMC4311807 DOI: 10.1073/pnas.1422509112] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We developed a microscopic theory for the point-contact conductance between a metallic electrode and a strongly correlated material using the nonequilibrium Schwinger-Kadanoff-Baym-Keldysh formalism. We explicitly show that, in the classical limit, contact size shorter than the scattering length of the system, the microscopic model can be reduced to an effective model with transfer matrix elements that conserve in-plane momentum. We found that the conductance dI/dV is proportional to the effective density of states, that is, the integrated single-particle spectral function A(ω = eV) over the whole Brillouin zone. From this conclusion, we are able to establish the conditions under which a non-Fermi liquid metal exhibits a zero-bias peak in the conductance. This finding is discussed in the context of recent point-contact spectroscopy on the iron pnictides and chalcogenides, which has exhibited a zero-bias conductance peak.
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Affiliation(s)
- Wei-Cheng Lee
- Department of Physics, University of Illinois, Urbana, IL 61801
| | - Wan Kyu Park
- Department of Physics, University of Illinois, Urbana, IL 61801
| | - Hamood Z Arham
- Department of Physics, University of Illinois, Urbana, IL 61801
| | - Laura H Greene
- Department of Physics, University of Illinois, Urbana, IL 61801
| | - Philip Phillips
- Department of Physics, University of Illinois, Urbana, IL 61801
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Escudero R, López-Romero RE, Morales F. Study of the hidden-order of URu₂Si₂ by point contact tunnel junctions. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:015701. [PMID: 25469859 DOI: 10.1088/0953-8984/27/1/015701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
URu2Si2 presents superconductivity at temperatures below 1.5 K and a hidden order (HO) at about 17.5 K. Both electronic phenomena are influenced by Fano and Kondo resonances. At 17.5 K the HO was related in the past to a Peierls distortion that produces an energy gap deformed by the resonances. This order has been studied for more than 20 years and still there is no clear understanding. In this work we studied the electronic characteristics of URu2Si2 in a single crystal, with tunneling and metallic point contact spectroscopies. In the superconducting state, we determined the energy gap, which shows the influence of the Fano and Kondo resonances. At temperatures where HO is observed, the tunnel junctions spectra show the influence of the two resonances. Tunnel junction characteristics show that the Fermi surface nesting depends on the crystallographic direction.
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Affiliation(s)
- R Escudero
- Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México. A. Postal 70-360, 04510 México city, DF, Mexico
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Arnold F, Yager B, Kampert E, Putzke C, Nyéki J, Saunders J. Spear-anvil point-contact spectroscopy in pulsed magnetic fields. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:113901. [PMID: 24289405 DOI: 10.1063/1.4828657] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We describe a new design and experimental technique for point-contact spectroscopy in non-destructive pulsed magnetic fields up to 70 T. Point-contact spectroscopy uses a quasi-dc four-point measurement of the current and voltage across a spear-anvil point-contact. The contact resistance could be adjusted over three orders of magnitude by a built-in fine pitch threaded screw. The first measurements using this set-up were performed on both single-crystalline and exfoliated graphite samples in a 150 ms, pulse length 70 T coil at 4.2 K and reproduced the well known point-contact spectrum of graphite and showed evidence for a developing high field excitation above 35 T, the onset field of the charge-density wave instability in graphite.
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Affiliation(s)
- F Arnold
- Royal Holloway, University of London, Egham TW20 0EX, United Kingdom
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Chandra P, Coleman P, Flint R. Hastatic order in the heavy-fermion compound URu2Si2. Nature 2013; 493:621-6. [PMID: 23364741 DOI: 10.1038/nature11820] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Accepted: 11/27/2012] [Indexed: 11/09/2022]
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Si Q. Hidden is more. Nature 2013; 493:619-20. [DOI: 10.1038/493619a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Optical spectroscopy shows that the normal state of URu2Si2 is an anomalous Fermi liquid. Proc Natl Acad Sci U S A 2012; 109:19161-5. [PMID: 23115333 DOI: 10.1073/pnas.1208249109] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fermi showed that, as a result of their quantum nature, electrons form a gas of particles whose temperature and density follow the so-called Fermi distribution. As shown by Landau, in a metal the electrons continue to act like free quantum mechanical particles with enhanced masses, despite their strong Coulomb interaction with each other and the positive background ions. This state of matter, the Landau-Fermi liquid, is recognized experimentally by an electrical resistivity that is proportional to the square of the absolute temperature plus a term proportional to the square of the frequency of the applied field. Calculations show that, if electron-electron scattering dominates the resistivity in a Landau-Fermi liquid, the ratio of the two terms, b, has the universal value of b = 4. We find that in the normal state of the heavy Fermion metal URu(2)Si(2), instead of the Fermi liquid value of 4, the coefficient b = 1 ± 0.1. This unexpected result implies that the electrons in this material are experiencing a unique scattering process. This scattering is intrinsic and we suggest that the uranium f electrons do not hybridize to form a coherent Fermi liquid but instead act like a dense array of elastic impurities, interacting incoherently with the charge carriers. This behavior is not restricted to URu(2)Si(2). Fermi liquid-like states with b ≠ 4 have been observed in a number of disparate systems, but the significance of this result has not been recognized.
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