Calorimetric study of YBa2Cu3O6.92 in very high magnetic field: 27 Tesla

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<ul><li><p>Physiea C 235-240 (1994) 1763 - 1764 North-Holland PHYSICA </p><p>Calorimetric Study of YBa2Cq306.92 ia Very High Magnetic Field: 27 Tesla </p><p>E. Janod t,2, C. Marcenat l, C. Baraduc t, A. Junod 2, R. Calemczuk l, G. Deutscher 3 and J.-Y. Hem'y 2 1CEA/D6partement de Recherche Fondamentale sur la Matl~re Condens6e, 38054 Grenoble Cedex 9, France 2 D6partement de Physique de la Mati~re Condensde. 24 quai E.-Ansermet, CH-1211 Gen~ve 4, Switzerland. 3 Universit6 de Tel-Aviv, Tel-Aviv, Israel </p><p>The specific heat of a large YBa2Cu30 6 92 single crystal (m=150 mg) was measured between 0 and z7 Tesla. In contrast with previous results obtained at lower fields, the specific heat above T c ~s field-dependent up to 100 K The high magnetic fields combined with a narrow transition mdth (ATcI0"90%=0 15 K in ac susceptibihty) allow an accurate analys~s of the different conmbuuons in the vicinity of To(H=0), 2D-3D gaussian and 3D-xy critical fluctuations models are compared A posmve curvature of the Hc2(T) hne is observed up to 10 Tesla. The compaUbility of the calorimetric and magnetic measurements [1] through Maxwell's relation ~s also verified </p><p>Only few specific heat data under high magneUc fields have been pubhshed for single cry~talhne YBa2Cu3Ox (Y-123) High fields and high resolution measurements may however help to understand its thermodynanuc properUes, the nature of superconducting fluctuations close to Tc or the strength of the electron-boson couphng </p><p>A large (ln=150 mg) porous Y-123 single cr3 stal was synthesized using a recrystallisation technique The final treatment at 460C in mr during 120 hours was follo~ed by a quench, resulting in a sharp transition and an optimized Tc (92.6 K) Specific heat was measured up to 14 m a superconducting coil and 27 T in an hybrid magnet The calorimeter is of continuous heating type </p><p>The specific heat measured between 0 and 27T (H//c) is clearly field-dependent above Tc (Fig la) The high fields therefore allow a direct observatlOla of fluctuations up to 100 K The anomaly is observable even for ~toH=27 T (Fig lb) ff the lattice specific heat shown in Fig la and described m Table 1 is subtracted A pseudo Hc2(T) line ~s n,.~,.~n us ing thc ilhqCkiOn puntt~ of t,,..-,~ph)t i Oit the right side of the anomaly One can remark m the insert of Fig lb the difficulty to find a hnear slope close to T c An interesting fact is the unusual He2 dependence predicted m the crmcal legion [2,3] where Hc2c~t 4/3 Th~s behav~our (solid hne) agrees ruth our Hc2(T) dctermumtlon up to 10-14T The extrapolaUon at T=0 K of the average slope ~to(dHc, c/dF)=-3 2 T/K (dashed hnc) gp,'cs p.oHc2.~ ~L=. 96 T and therefore V~ohGL=167-195 A s, </p><p>0 108 </p><p>,-, 0106 </p><p>0104 </p><p>0102 </p><p>01 75 80 85 90 95 100 105 </p><p>0 006 </p><p>~m 0,0045 </p><p>~, 0 003 </p><p>"- b </p><p>0 . . . . . . </p><p>83 88 9~_. Temperature ( K ~ </p><p>00015 . . . . : . . . . ', . . . . : . . . . -~ 60 70 80 9O 100 </p><p>Temperature (K) Fig 1 (a) C/T under 0,1,6.14.27 T (I-U/c), Co) C/T under 0.1,3,6,10,14,27 T after subtracuon of the lattice specific heat, (insert) Hc2(T) with Tc2(H) = InflcXlOD polnl ort lhe right side of lhe anomaly </p><p>considering an amsotrop) ratio of C to 7 </p><p>0921-4534/94 507 00 1994 - Elsevier Science B V All rights rccrvcd S5;DI f021-4 ~4(94)01448-5 </p></li><li><p>1764 E Janod et al /Phystca C 235-240 (1994) 1763-1764 </p><p>0 004 </p><p>0 003 </p><p>~- 0.0o2 </p><p>0 001 </p><p>0 </p><p>-0 001 . . . . : . . . . : . . ~ , ~ . . . , . . . . ~ . . . . </p><p>50 60 70 80 90 100 110 </p><p>Temperature (K) Fig 2: [C(0)-C(~H)I/T vs T (~H=6,14,27T, H//c) In this representation, the difference AC/T=(Ces - Cen)/T between the electronic superconducting and normal specific heat ts recovered for H=Hc2x(0) </p><p>The zero-field elect,,'mc specific heat may be roughly estimated by extrapolating the (C(0)- C(B))/T representation (Fig. 2) to higher fields in ordcr to obtain a curve Lsohd hne) that preserves the equality of entropies betx~een the normal and superconducting states The mean-field contribution (dashed line) is obtained by constdermg that fluctuations below or above T c are s.x mmctrlcal or in a ~/2 ratm [2,31 The ratto d(AC/dT)/(AC/Tc) between the mean-field slope below T c and the jump is near 3.1-3.85 mvoh'mg a AC/(~,T c) of 1 8-2 35 following the model of Mars~gllo, Ak~J and Carbotte [4] These values are conststent ~sth a moderately strong elcctron-boson coupling </p><p>Zero field data were fitted omatmg a x~ mdcxx AT* of variable width near To. A funcUonal formed by a lattice part Cph(T) including three Emstein contnbutmns (Cph/3R=Y-(D~E(0/T)), E(x)=x2eV(e \- 1) 2) and an electromc part Ce(T) Is used The latter consists of a mean-field (nff) Cmr and a fluctuation C n contributions The two-fltnds model(Cn~ -2"llulds) was used for the mf part rather than the BCS one ~h~ch gives poorer results Critical fluctuations (Cfl crtt) consistent with a 3D-xw model [21 and Gaussiaa fluctuatmns (cl~gauss) vahd farther front T c o~ tlleorporouasl~, a I .&amp;l l l l~,| i~lt~.. l l lOl ~ l%? .~oO]e l upon approaching T [31 are compared </p><p>o It log kB ,CI] = Coln(t) </p><p>t=ll-T/Tci, a=i abo~e T c anJ 2 below, b=2~. Jc. c 1~ </p><p>013 </p><p>~n01 </p><p>0.07 </p><p>0.04 </p><p> model a </p><p>---c--- model b Ik </p><p>o . </p><p>0.1 1 10 </p><p>AT* (K) Fig. 3: evolution of the residual of the fit o vs AT* </p><p>the interlayer distance, V OL= ~,~:GL~2y:GL is the coh ~"~ab j ~c </p><p>Gmzburg-Landau coherence volume and C O is an amphtude term. </p><p>Fig.3 shows the evolution of the standard devmtion o of the fit vs AT* for two scenarios, (a) Cph C2fltUdSraf +L.fl ,-,gauss , (b) Cp h + C2fluidstaft -I- I..fl ,-,crit log </p><p>The quality, of the fit clearly decreases for AT*</p></li></ul>


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