Display the Experiment Proposals

Experiment: M1138

Search for Weak Magnetism in Cuprates

by the none group

Active (Stage 2)
Spokespersons:
J.E. Sonier (Simon Fraser University)

Progress Report for EEC meeting 200912M

Table of Contents

Detailed Information

Complete/Merged PDF M1138_200912M_merged.pdf
Form data only M1138_200912M.pdf
Detailed Statement M1138_Detailed_Statement_2009.pdf (122.32 kB)

Beam Shift Summary

12-hr ShiftsBeam Line / channelPriority
New Beam Requests
 24 M15

Low-temperature μSR measurements on heavily overdoped La2-xSrxCuO4 single crystals using the dilution refrigerator.

12 M15

High transverse-field (TF) μSR measurements (7 T) on heavily overdoped La2-xSrxCuO4 and (Y,Ca)Ba2Cu3Oy single crystals using Hi-Time.  

12 M15

High-temperature (2 K < T < 250 K) ZF-μSR measurements on heavily overdoped La2-xSrxCuO4 single crystals using a helium-gas flow cryostat.

Committee Recommendations
 24 MH

This is a continuation of an experimental programme which originally aimed to investigate the possibility of so-called loop current order in Y and La based cuprate superconductors. µSR measurements failed to provide any evidence for this phenomenon. The proposers now wish to shift their attention to the possible existence of ferromagnetic correlations in heavily overdoped La2-xSrxCuO4 and (Y,Ca)Ba2Cu3Oy single crystals, and study the role of such correlations in the suppression of the superconducting state. While it is surprising that such studies have not been performed previously, and although evidence for such correlations is rather flimsy, it is clear that µSR is perhaps the ideal probe for weak ferromagnetism in the overdoped superconducting regime. The group will have well prepared and characterized samples for their study. Although speculative, the Committee thought the proposed measurements were both feasible and worthwhile.

Beam Shifts Used
 9 M20

Used on Schedule 117.

0

22 more shifts scheduled on Schedule 117.

Beam Shifts Remaining
 26 -

As of May 27, 2010.


Membership

J.E. Sonier Simon Fraser University Professor 25 % Spokesperson
W. Huang Simon Fraser University Student (Graduate) 50 %  
C.V. Kaiser Simon Fraser University Student (PhD) 20 %  
N.E. Hussey University of Bristol Professor 10 %  
S. Komiya CRIEPI Staff Member 10 %  
D.A. Bonn University of British Columbia Professor 5 %  
R. Liang University of British Columbia Research Associate 5 %  
W.N. Hardy University of British Columbia Professor 5 %  

Basic Information

Date Submitted
2009-11-08 17:09:43
Date Experiment Ready
2009-11-08
Summary *

The initial goal of M1138 was to search for evidence of loop-current order in the so-called pseudogap region of high-Tc cuprate superconductors. The detection of loop-current order in the CuO2 layers would be a confirmation of theories that ascribe the pseudogap region to a competing state that breaks time-reversal symmetry. The predicted local magnetic fields are sizeable, and should be easily detected by μSR. We have now completed a comprehensive search for this kind of magnetic order in two different cuprate systems, YBa2Cu3Oy and La2-xSrxCuO4, and find no evidence of loop-current order in either material.

Our interest has now shifted to an investigation of magnetism in the heavily overdoped regime to understand why superconductivity weakens and eventually disappears at high charge carrier concentration. One idea is that antiferromagnetic spin fluctuations are the “glue” that binds electrons into Cooper pairs in the superconducting state, and that these vanish at high doping. A second intriguing possibility is that ferromagnetic fluctuations compete with superconductivity in the overdoped regime. In this scenario, a ferromagnetic phase is predicted to exist beyond the doping concentration at which superconductivity disappears. This mean that the superconducting phase is sandwiched between a competing antiferromagnetic phase at low doping levels, and a competing ferromagnetic phase at high doping levels. We have begun to explore this issue, and preliminary measurements on samples in the heavily overdoped regime offer some support to this hypothesis. It is not easy to prepare heavily overdoped non-superconducting samples, and is impossible in many of the cuprate systems. Nevertheless, small single crystals of La2-xSrxCuO4 do exist in this regime, and we have demonstrated that they can be studied by μSR.

Plain Text Summary *
The current goal of this experiment is to understand why high-temperature superconductivity weakens and eventually disappears at high charge carrier concentration in cuprate materials. One possibility is that there exists a competing ferromagnetic phase in the heavily overdoped regime. The technique of muon spin relaxation, which uses positive muon beams at TRIUMF, is well suited to investigate this hypothesis.
Primary Beam Line
Base 1A
Secondary Channel
Base
M15
Primary / Secondary Beam
Energy (MeV)
500(MeV)
Intensity (uA)
100(uA)
Production Target
Summary List of samples

La2-xSrxCuO4

(Y,Ca)Ba2Cu3Oy

μSR Spectrometers
DR (Pandora), High-Time, LAMPF
TRIUMF Support (Resources Needed)
NSERC

User fees and helium charges will be paid for with funds from an individual NSERC discovery grant.

Other Funding
Muon Justification

Our preliminary results indicate that there is static magnetism in the heavily overdoped regime, but it is dilute. As a pure local magnetic probe, μSR is ideally suited for studies of dilute moment systems.

Safety Issues

There are no unusual safety issues associated with this proposal.

Proposals and Progress Reports

200912M
200706M (Original Proposal)