BS-04 Muon Probing and Magnetism in Cuprate Superconductors
Creators: C Boekema
Publisher: name: IEEE
Year: 2025

There are still questions as to how and where the muon probes magnetism in cuprates. Shekhter et al [1] found that using a metal approach, the muon charge reduces or destroys pseudogap loop currents. [2] Yet, Dawson’s muon-site search [3] indicated candidates only in insulating regions of these quasi-2-dim superconductors RBa2Cu3O7-d (RBCO). Sio et al [4] studied the muon sites in GdBCO by using Maximum Entropy [5] (MaxEnt, ME) to analyze transverse field (TF) muon-spin-rotation (µSR) GdBCO data. We have improved upon this MEµSR study. The Balmer (B1 & B2) sites and Lin (L1, L2 & L3) sites are located in RBCO, ~1 Å away from O2- ions. B1 & B2 are near the BaO layer; [3] B2 is the favorite site. L1, L2 and L3 are near or in the CuO-chain layer. [4,6] At & below RT, muons localize at these B/L sites, depending on local potential energy and their thermal hopping energy. For both underdoped GdBCO (d1, Tc = 81 K) and optimal doped GdBCO (d0; Tc = 93 K) TFµSR data [7] were recorded at and below RT at 100-Oe and 1-kOe fields. MEµSR analysis (being more sensitive [5] than FT & curve fitting) is performed.The best ME fits include two Lorentzians (Lor) & one Gaussian (Gau) for the grain boundary. These ME results are consistent with muon occupancy of B2 and B1/Lin sites. [3,8] When B1 and Lin positions are near a positive O vacancy (repelling m+ probes) these sites become less stable in underdoped GdBCO(d1). As T increases, this effect is more pronounced. At 120 K three signals are visible in underdoped GdBCO(d 1), yet at RT only one dominant signal remains. In contrast, two Lorentzian signals are present at 120 K and at RT for GdBCO(d0), where there are significantly less O vacancies. Thus, the muon localizes in an undisturbed insulating environment away from the CuO2 planes and measures (weak) magnetic fields of Sharma’s pseudogap loop currents. [2,6,8,9]References: [1] A Shekhter et al, Phys Rev Lett 101 (2008) 227004. [2] CM Varma, PRL 83 (1999) 3538; ME Simon & CM Varma, PRL 89 (2002) 247003; IM Vishik et al, Proc Nat Acad Sci 109 (2012) 18332. [3] WK Dawson et al, J Appl Phys 64 (1988) 5809; Hpf Int 63 (1990) 219. [4] H Sio, MC Browne et al, APS March meeting (2011) & SJSU internal report. [5] C Boekema and MC Browne, MaxEnt 2008, AIP Conf Proc #1073 pp260-267. [6] C Boekema et al, Physica C493 (2013) 136. [7] DW Cooke et al, Phys Rev B37 (1988) 9401. [8] T Songatikamas et al, J Spcd & Nvl Magn 23 (2010) 793. [9] C Boekema et al, J Modern Physics B29 (2015) 1542026.
There are still questions as to how and where the muon probes magnetism in cuprates. Shekhter et al [1] found that using a metal approach, the muon charge reduces or destroys pseudogap loop currents. [2] Yet, Dawson’s muon-site search [3] indicated candidates only in insulating regions of these quasi-2-dim superconductors RBa2Cu3O7-d (RBCO). Sio et al [4] studied the muon sites in GdBCO by using Maximum Entropy [5] (MaxEnt, ME) to analyze transverse field (TF) muon-spin-rotation (µSR) GdBCO data. We have improved upon this MEµSR study. The Balmer (B1 & B2) sites and Lin (L1, L2 & L3) sites are located in RBCO, ~1 Å away from O2- ions. B1 & B2 are near the BaO layer; [3] B2 is the favorite site. L1, L2 and L3 are near or in the CuO-chain layer. [4,6] At & below RT, muons localize at these B/L sites, depending on local potential energy and their thermal hopping energy. For both underdoped GdBCO (d1, Tc = 81 K) and optimal doped GdBCO (d0; Tc = 93 K) TFµSR data [7] were recorded at and below RT at 100-Oe and 1-kOe fields. MEµSR analysis (being more sensitive [5] than FT & curve fitting) is performed.The best ME fits include two Lorentzians (Lor) & one Gaussian (Gau) for the grain boundary. These ME results are consistent with muon occupancy of B2 and B1/Lin sites. [3,8] When B1 and Lin positions are near a positive O vacancy (repelling m+ probes) these sites become less stable in underdoped GdBCO(d1). As T increases, this effect is more pronounced. At 120 K three signals are visible in underdoped GdBCO(d 1), yet at RT only one dominant signal remains. In contrast, two Lorentzian signals are present at 120 K and at RT for GdBCO(d0), where there are significantly less O vacancies. Thus, the muon localizes in an undisturbed insulating environment away from the CuO2 planes and measures (weak) magnetic fields of Sharma’s pseudogap loop currents. [2,6,8,9]References: [1] A Shekhter et al, Phys Rev Lett 101 (2008) 227004. [2] CM Varma, PRL 83 (1999) 3538; ME Simon & CM Varma, PRL 89 (2002) 247003; IM Vishik et al, Proc Nat Acad Sci 109 (2012) 18332. [3] WK Dawson et al, J Appl Phys 64 (1988) 5809; Hpf Int 63 (1990) 219. [4] H Sio, MC Browne et al, APS March meeting (2011) & SJSU internal report. [5] C Boekema and MC Browne, MaxEnt 2008, AIP Conf Proc #1073 pp260-267. [6] C Boekema et al, Physica C493 (2013) 136. [7] DW Cooke et al, Phys Rev B37 (1988) 9401. [8] T Songatikamas et al, J Spcd & Nvl Magn 23 (2010) 793. [9] C Boekema et al, J Modern Physics B29 (2015) 1542026.