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Charge Density Wave and Superconductivity: Investigation on the Coexistence, Coupling and Competition of the Two Ground States

English title Charge Density Wave and Superconductivity: Investigation on the Coexistence, Coupling and Competition of the Two Ground States
Applicant Khasanov Rustem
Number 175935
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Condensed Matter Physics
Start/End 01.01.2018 - 31.12.2020
Approved amount 313'240.00
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Keywords (4)

muon-spin rotation/relaxation; pressure effect; charge density wave; superconductivity

Lay Summary (German)

Lead
LeadIn unserem Projekt untersuchen wir im Detail die Koexistenz und Wechselwirkung zwischen Ladungsdichtewellen und Supraleitung. Verschiedene Materialien werden dabei mit der lokalen Sondentechnik der Myonenspinrotation und makroskopischen Techniken wie DC und AC Magnetometrie und Widerstandsmessungen untersucht.?
Lay summary
Inhalt und Ziele

Supraleitung entsteht oft in Materialien in denen konkurrierende Grundzustände wie Antiferromagnetismus oder Ladungsdichtewellen vorkommen. Normalerweise wechselwirken diese Zustände stark miteinander. Diese Wechselwirkungen stellen die modern Festkörpertheorie for starke Probleme insbesondere bei dem Verständins des supraleitenden Mechanismus.  

Um dieses komplexe Problem anzugehen ist es von herausragender Bedeutung die Untersuchungen mit einfachen Modelsystemen, in denen nur wenige dieser Zustände konkurrieren, zu beginnen. In diesem Projekt untersuchen wir deshalb Materialien in denen die Supraleitung nur mit der Ladungsdichtewelle konkurriert.

 

Wissenschaftlicher und gesellschaftlicher Kontext

Unsere Grundlagenforschung ist von fundamentalem Interesse für die Festkörperphysik. Die vorgeschlagenen Experimente werden wertvolle Informationen bezüglich der Wechselwirkung der verschiedenen Ordnungsphenomäne liefern. Besondere Aufmerksamkeit soll hier auf Bereiche der Phasendiagramme gelegt werden in denen Quantenphasenübergänge (Übergänge bei 0 Kelvin) zwischen den verschiedenen Phasen zu beobachten sind. Diese Untersuchungen werden somit wichtige Informationen zu den Wechselwirkungen zwischen Ladungsdichtewellen und dem Auftreten der Supraleitung liefern.

 

Direct link to Lay Summary Last update: 30.11.2017

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Abstract

We propose a detailed investigation of the coexistence and interplay between charge-density wave (CDW) and superconducting (SC) ground states. Our project includes the study of various compounds using the internal local probe technique muon-spin rotation (µSR), as well as macroscopic techniques such as DC and AC magnetization and transport experiments. The combination of different experimental techniques will allow us to obtain the SC and CDW responses at both the microscopic and macroscopic levels. To minimize the influence of disorder effects, we plan to use hydrostatic pressure as the main tuning parameter between the two ground states. Our study will be mainly focused on the regions of phase diagram boundaries and on the quantum critical points (QCPs) where CDW and SC meet. The superconducting condensate and the superconducting order parameter symmetry are planned to be studied within the full pressure-temperature phase diagram, i.e., where both SC and CDW orders coexist and where one of the orders gets fully suppressed. The following subprojects are planned to be performed in the realm of this general research topic: (i) Tuning of SC and CDW order in TlxV6S8: This system is characterized by a nonmonotonic superconducting transition temperature (Tc) versus pressure (p) dependence, which is associated with the suppression of the CDW order. We have specifically chosen this system as the situation resembles very much the one observed in the simplest iron-based high-temperature superconductor (HTS) FeSe, where a similar Tc versus p behavior is caused by an interplay between a density wave due to the spin-degrees of freedom (SDW) and the SC state. The goal of the proposed research is to precisely investigate the similarities and/or differences between both the CDW/SC and the SDW/SC interplay. (ii) Pressure effects within the phase diagram of the pristine and Cu intercalated 1T-TiSe2: The dependence of Tc on x in CuxTiSe2 as well as on the applied pressure in pristine 1T-TiSe2 both show a dome-like structure characteristically found in phase diagrams of cuprate and iron-based HTSs, heavy fermions and layered organics. The case of 1T-TiSe2 signals the possibility of a novel state, where superconductivity emerges out of a new type of QCP, unrelated to magnetic degrees of freedom. Experiments under pressure will allow us to perform a fine tuning of both the SC and the CDW states and, therefore, to make a precise study of the investigated compounds in the close vicinity to the QCP. (iii) Influence of CDW on the order parameter symmetry: The symmetry of the superconducting order parameter is a key for understanding the pairing mechanism of the superconducting ground state. To date, the d-wave pairing in cuprates and the predominately s? superconducting state in iron-based HTSs is generally established. There is, however, no agreement on the order parameter symmetry in materials where superconductivity coexists with CDW order. We therefore plan to investigate in detail the evolution of the superconducting gap(s) symmetry caused by the suppression of CDW order in Ta4Pd3Te16 and 2H-NbSe2. The project aims to create a strong initiative in Switzerland for the experimental study of various CDW and SC materials using muon-spin rotation (µSR) under hydrostatic pressure conditions. The collaborative work will be built around members of the Laboratory for Muon Spin Spectroscopy at the Paul Scherrer Institute (PSI) and some national and international partners. Important interactions are expected with the Laboratory for Scientific Developments and Novel Materials at PSI (Dr. E. Pomyakushina), the University of Bern (Dr. N. Zhigadlo), and the Ames Laboratory at the Iowa State University (Prof. Paul Canfield and Dr. S. Budko).
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