Tuning the Superconducting Gap Symmetry in Ba1-xRbxFe2As2 by Hydrostatic Pressure
Zurab Guguchia
Laboratory for Muon Spin Spectroscopy, Paul-Scherrer Institut, Switzerland
Hubertus Luetkens
Tbilisi
SokhumiIlia Vekua Sukhumi Institute of Physics and Technology (SIPT)
სოხუმის ილია ვეკუას სახელობის ფიზიკა-ტექნიკის ინსტიტუტი
Sokhumi Hubertus Luetkens
Thank you!
Laboratory for Muon Spin Spectroscopy (PSI) Hugo Keller Fabian von Rohr
Rustem Khasanov Biswas
Alex Amato
Pabitra
Elvezio Morenzoni
Hubertus Luetkens
Tbilisi State University Rafael Fernandes Jian Kang
Alexander Shengelaya Tornike Qimeridze Ana sliusareva
Giacomo Prando Ludwig-Maximilians-University of Munich
Dirk Johrendt Erwin Wiesenmeyer Hubertus Luetkens
Institute of Low Temperature and Structure Research
Zbigniew Bukowski
µSR
Bµ
Bµ internal or external field Hubertus Luetkens
aPx (t) ~ Muon Spin Polarization
μSR Spectra
Hubertus Luetkens
Frequency Frequency Value Valueofoffield field atatmuon muonsite site (ω (ωL L==γγmmBBmm)) Damping Damping Field Fielddistribution distribution and/or and/ordynamics dynamics
µ SR ⇒ local magnetic field distribution p(B) in the mixed state of a type II sc H Hc2
Hc1 Tc
Bext
Bext Since the muon is a local probe, the µSR relaxation function is given by the weighted sum of all oscillations:
P(t) Hubertus Luetkens
μSR technique
second moment of p(B) 2
-4
2 -4 ∆B ∆B ∝∝ λλ
Gaussian distribution p(B)
σ ∝ ∆B2
1/2
∝ 1 / λ2 ∝ ns / m*
σ : µSR relaxation rate Hubertus Luetkens
s-wave Superconducting Gap • BCS conventional pairing: isotropic s-wave pairing
B. MĂźhlschlegel, Z. Phys. 155, 313 (1959)
Hubertus Luetkens
s-wave gap
d-wave Pairing Symmetry
Ď•
Single crystal YBa2Cu3O6.95 J.E. Sonier et al, PRL 72, 744 (1994) Hubertus Luetkens
GPD spectrometer (Âľ E1 beamline)
Positive or negative muons: momentum ranges ~60-125MeV/c. Muon range: ~1.5-20g/cm2, range width ~30mg/cm2-~4g/cm2 FWHM in CH2. Polarization: Longitudinal (direction of the muon momentum; no spin rotation). Hubertus Luetkens
Momentum acceptance (FWHM) 3% Pion momentum range [MeV/c] 200--125 Muon momentum range [MeV/c] 125-- 60 Rate of positive muon [mA-1s-1] 6e7--3e7 Spot size (FWHM) 39 X 28 mm
double-wall cells AC cryostat
Material: CuBe, MP35N, Al2O3 Pressure range: up to ~2.3 GPa (normal operation) Temperature range: 0.25K—300K
P ≈ 27 kbar Fraction of the muons in the sample ~ 50 % Hubertus Luetkens
Different families of Fe-HTS‘s
Hubertus Luetkens
Phase Diagrams of Fe-HTS’s
H. Luetkens et al., Nature Materials 8, 305 (2009)
E. Wiesenmayer et al., Phys. Rev. Lett. 107, 237001 (2011)
J.-H. Chu et al., Phys Rev B 79, 014506 (2009)
CaFe2As2
A. Kreyssig et al., Phys. Rev. B 78, 184517 (2008) M.S. Torikachvili et al., Phys. Rev. Lett. 101, 057006 (2008) Hubertus Luetkens
Z. Guguchia et. al., Phys. Rev. B 83, 144516 (2011). Z. Guguchia et. al., JPCM 26, 285 (2013).
Central issue What is the microscopic pairing mechanism in the Fe - HTS's?
Identifying the SC gap symmetry/structure of the Fe-HTS’s?
Hubertus Luetkens
Multiband Superconductivity ARPES on Ba1-xKxFe2As2:
• Multiband superconductivity • Nodeless gaps
∆1 = 2.7(5) meV and ∆ 2 = 8.4(3) meV. V. B. Zabolotnyy et al., Nature 457, 569 (2009). D. V. Evtushinsky et al.,Phys. Rev. B 79, 054517 (2009). D. V. Evtushinsky et al., New J. Phys. 11, 055069 (2009). Hubertus Luetkens
Z. Guguchia et al., Phys. Rev. B 84, 094513 (2011).
Non universal SC gap structure in Fe-based high-temperature superconductors Ba1-xKxFe2As2, Ba1-xRbxFe2As2 BaFe2-xNixAs2, BaFe2-xCoxAs2 KxFe2-ySe2, FeTe1-xSex
LaOFeP, LiFeP, KFe2As2, BaFe2(As1-xPx)2 BaFe2-xRuxAs2, Over-doped Ba1-xKxFe2As2
J-Ph. Rheid et. al., Supercond. Sci. Technol. 25, 084013 (2012). M. Abdel-Hafiez et. al., arXiv: 1502.07130v1 (2015). Y. Zhang et. al., Nature Physics 8, 371-375 (2012). M.S. LaadLuetkens et. al.,, Phys. Rev. Lett. 103, 017002 (2009). Hubertus
Phase diagram of Ba1-xRbxFe2As2
Z. Guguchia et al., manuscript under preparation (2015). Hubertus Luetkens
S. Peschke et al., JIGC 640, 830-835 (2014).
ÂľSR time spectra and Fourier transforms for optimally doped Ba 1-xRbxFe2As2 (x = 0.35)
Z. Guguchia et al., Nature Comm. (2015). Hubertus Luetkens
Diamagnetic shift and the muon spin relaxation rate for optimally doped Ba1-xRbxFe2As2 (x = 0.35)
∆Bdia = µ 0 [ H int, SC − H int, NS ] T / Tc ≈ 0.4
Gaussian distribution p(B)
σ ∝ ∆B2
1/2
∝ 1 / λ2 ∝ ns / m*
σ : µSR relaxation rate
Z. Guguchia et al., Nature Comm. (2015). Hubertus Luetkens
Temperature and pressure dependent magnetic penetration depth in optimally doped Ba1-xRbxFe2As2 (x = 0.35)
No nodes in the SC-gap Nodes in the SC-gap
Nodes: Are they accidental or imposed by symmetry?
λ−2 (T , ∆ 0,1 ) λ−2 (T , ∆ 0, 2 ) λ−2 (T ) = ω1 − 2 + ω2 −2 λ− 2 (0) λ (0, ∆ 0,1 ) λ (0, ∆ 0, 2 )
Constant gap - ∆ 0,i = ∆ i . Angle dependent gap - ∆ 0,i = ∆ i cos(2ϕ ).
∆1 = 2.7(5) meV and ∆ 2 = 8.4(3) meV. Z. Guguchia et al., Nature Comm. (2015).
Hubertus Luetkens
Z. Guguchia et al., Phys. Rev. B 84, 094513 (2011).
Three pocket model used in calculations
Z. Guguchia et al., Nature Comm. (2015). Hubertus Luetkens
Temperature and pressure dependent magnetic penetration depth in optimally doped Ba1-xRbxFe2As2 (x = 0.35)
Z. Guguchia et al., Nature Comm. (2015). Hubertus Luetkens
Density plot of the gap function for the d − wave state
Z. Guguchia et al., Nature Comm. (2015). Hubertus Luetkens
Possible explanations for the pressure induced nodes in optimally doped Ba1-xRbxFe2As2 (x = 0.35)
• •
In optimally doped Ba0.6K0.4Fe2As2 a sub-dominant d-wave state close in energy to the +− dominant s state was found. A systematic comparison of quasiparticle excitations in the 1111, 122, and 111 families of iron-pnictide superconductors implies that the nodal state may be induced when the pnictogen height from the iron plane decreases below a threshold value of 1.33 Å.
S. Maiti et. al., Phys. Rev. Lett. 107, 147002 (2011). R. Thomale et. al., Phys. Rev. Lett. 107, 117001 (2011). T. Bohm et. al., Phys. Rev. X 4, 041046 (2014). Hubertus Luetkens
Pressure dependence of various quantities of optimally doped Ba1-xRbxFe2As2 (x = 0.35)
Z. Guguchia et al., Nature Comm. (2015). Hubertus Luetkens
K. Hashimoto et al., Science 336, 1554 (2012). P. Walmsley et. al., Phys. Rev. Lett. 110, 257002 (2013).
Temperature and pressure dependent magnetic penetration depth in over-doped Ba1-xRbxFe2As2 (x = 0.65)
Z. Guguchia et al., manuscript under preparation (2015). Hubertus Luetkens
Conclusions
s-wave d-wave
The SC transition temperature stays nearly constant under pressure, whereas a strong reduction of λ(0) is observed in Ba1-xRbxFe2As2 (x = 0.35). We demonstrated that in the Fe-based superconductor Ba1-xRbxFe2As2 (x = 0.35) a nodal SC gap is promoted by hydrostatic pressure. The SC gap symmetry as well as the pressure effects on the quantities characterizing the SC state strongly depends on the hole doping level x. Hubertus Luetkens
Thank you very much for your attention!
Hubertus Luetkens