Giorgi Ghambashidze Institute of Condensed Matter Physics, Tbilisi State University,

Giorgi Ghambashidze

Institute of Condensed Matter Physics, Tbilisi State University, GE-0128 Tbilisi, Georgia

Muon Spin Rotation Studies of the Pressure Effect on the Static Stripe Magnetic Order in the

La2-xBaxCuO4 (x=1/8) System

Collaboration

University of ZürichTbilisi State University

Prof. Alexander Shengelaya Zurab Guguchia

Introduction

• Suppression of Superconductivity in La2-xBaxCuO4 (x=1/8) System

A. R. Moodenbaugh et. al., PRB 38, 4596 (1987)

In 1995, using neutron scattering, it was found, that in some In 1995, using neutron scattering, it was found, that in some cuprate superconductors, including Lacuprate superconductors, including La2-x2-xBaBaxxCuOCuO44, doped , doped

holes form an array of charge and spin ordered stripes.holes form an array of charge and spin ordered stripes.

J.M. Tranquada, et. al., Nature, 375, 561 (1995)

Problem!

• What is the reason of stripes formation at low temperatures for x=1/8 concentration?

• One of the explanation is related to low-temperature structural phase transition

But the exact reason not yet known.

At Ambient pressure and room temperature LBCO (x=1/8) compound has the high-temperature tetragonal (HTT) structure.

On Cooling below THT, thestructure transforms to thelow-temperature orthorhombic (LTO) phase, and belowTLT one reaches the low--temperature tetragonal(LTT) phase – which can be one of the possible reason of stripes formation.

Pressure effect on structural phase transition

Recently it was shown that, it’s possible to suppress low-temperature tetragonal (LTT) structural phase transition in LBCO (x=1/8) compound by applying pressure, but the charge order (CO) continues to exist beyond pc (critical pressure). It was notshown how the magnetic order related with static stripes is affected by

pressure. It was our main purpose of research!

M. Hucker at. al., PRB 104, 057004 (2010)

Muon Spin Rotation TechniqueWhat are muons?

Why Muons?

Use their spin (magnetic moment) as a magnetic probe

• Sensitive and accurate magnetometer

• Measures internal field and its variations (distribution in space, variation in time)

• Application in superconductivity, magnetism, conductive polymers…

Muons Production

nppp

Muon Precession

3 cm in length is pure phase of the single crystal

Muons Production

Pressure Cell

001

We used cylindrical high pressure cell for applying high pressure. It is made of half hard beryllium-copper and has one close end. This type of pressure cell can be applied at maximum 25 kbar pressure.

X-ray diffraction pattern for La2-xBaxCuO4 sample

ZF- μSR spectra at 4 K temperature and under 15 kbar pressure

ZF- μSR spectra at 32 K temperature and under 15 kbar pressure

Obtained Results Internal Magnetic Field vs. Temperature

for different pressures

It is known, that structural phase transition is suppressed at 18.5 kbar!

Conclusions

• LTT structural-phase transition is not the reason of spin magnetic ordered stripes formation, since we suppressed structural transition under pressure in La2-xBaxCuO4 (x=1/8) system.• Magnetic order continues to exist. • Magnetic transition temperature only slightly decreased by applied pressure.• Therefore other mechanisms should be found which could lead to static stripe order in LBCO compound at 1/8 concentration.

Thanks For Attention!