The in-plane resistivity rho and thermal conductivity kappa of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior rho(T) approximately T{1.5} at H{c{2}}=5 T, and the development of a Fermi liquid state with rho(T) approximately T{2} when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field H{c{2}}. In zero field, there is a large residual linear term kappa{0}/T, and the field dependence of kappa_{0}/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.

The in-plane resistivity and thermal conductivity of the heavy-fermion superconductor Ce 2 PdIn 8 single crystals were measured down to 50 mK. A field-induced quantum critical point, occurring at the upper critical field H c2 , is demonstrated from the ðTÞ $ T near H c2 and ðTÞ $ T 2 when further increasing the field. The large residual linear term 0 =T at zero field and the rapid increase of ðHÞ=T at low field give evidence for nodal superconductivity in Ce 2 PdIn 8 . The jump of ðHÞ=T near H c2 suggests a first-order-like phase transition at low temperature. These results mimic the features of the famous CeCoIn 5 superconductor, implying that Ce 2 PdIn 8 may be another interesting compound to investigate for the interplay between magnetism and superconductivity. The interplay between magnetism and superconductivity has been a central issue for heavy-fermion superconductors [1], high-T c cuprates [2], and iron pnictides [3]. Among them, one particularly interesting case is the heavy-fermion superconductor CeCoIn 5 , with T c ¼ 2:3 K at ambient pressure [4]. Its superconducting gap has d-wave symmetry [5,6]. While there is no static magnetism in CeCoIn 5 at zero field, a field-induced antiferromagnetic (AF) quantum critical point (QCP) has been clearly demonstrated by resistivity and specific heat measurements [7,8]. Initially, it was very puzzling why the AF QCP is located right at the upper critical field H c2 .Meanwhile, the observations of first-order phase transition at low temperature and H c2 and a second magnetization and specific heat anomaly well inside the superconducting state have been interpreted as the signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state [5,[9][10][11][12]. The novel FFLO state with broken spatial symmetry was predicted in the 1960s [13,14], but it has never been experimentally verified before. The possible FFLO state at the low-temperaturehigh-field (LTHF) corner of the H À T phase diagram of CeCoIn 5 has stimulated extensive studies [15].More recently, NMR, neutron scattering, and muon spin rotation ( SR) experiments have provided clear evidence for a field-induced magnetism in this LTHF part of the phase diagram [16][17][18][19][20][21]. It was identified as a spin-density wave (SDW) order with an incommensurate modulation Q ¼ ð0:44; 0:44; 0:5Þ. Interestingly, this SDW order disappears in the normal state above H c2 , showing that magnetic order and superconductivity in CeCoIn 5 are directly coupled [16,17]. While this has nicely explained the field-induced AF QCP at H c2 [7,8], the physical origin of this LTHF superconducting Q phase is still under debate. For example, Yanase and Sigrist have suggested that the incommensurate SDW order is stabilized in the FFLO state by the appearance of the Andreev bound state localized around the zeros of the FFLO order parameter [22]. Aperis, Varelogiannis, and Littlewood have argued that the Q phase is a pattern of coexisting condensates: a d-wave singlet superconducting state, a staggered -triplet superconducting s...

We present the ultra-low-temperature heat-transport study of iron-based superconductors BaðFe 1Àx Ru x Þ 2 As 2 and BaFe 2 ðAs 1Àx P x Þ 2 . For optimally doped BaðFe 0:64 Ru 0:36 Þ 2 As 2 , a large residual 0 =T at zero field and a ffiffiffiffi ffi H p dependence of 0 ðHÞ=T are observed, which provide strong evidences for nodes in the superconducting gap. This result demonstrates one more nodal superconductor in iron pnictides. The similarities between isovalent Fe and P dopings strongly suggest that the nodal superconductivity in Since the discovery of high-T c superconductivity in iron pnictides [1,2], the issue of what mechanisms underlie the electron pairing in these systems has been a central one [3]. One key step in resolving it is to clarify the symmetry and structure of the superconducting gap [4]. However, even for the most studied ðBa; Sr; Ca; EuÞFe 2 As 2 (122) system, the situation is still fairly complex [4].Near optimal doping where the T c is the highest, for both hole-and electron-doped 122 compounds, the angleresolved photon-emission-spectroscopy (ARPES) experiments have clearly demonstrated multiple nodeless superconducting gaps [5,6]. Those experiments have been further supported by measurements of bulk properties such as thermal conductivity [7][8][9]. On the overdoped (with respect to the optimal doping) side, nodal superconductivity has been found in the extremely hole-doped KFe 2 As 2 [10,11], while a strongly anisotropic nodeless gap [9] or isotropic nodeless gaps with significantly different magnitudes [12,13] have been suggested in heavily electron-doped BaðFe 1Àx Co x Þ 2 As 2 . On the underdoped side, recent heat-transport measurements have claimed possible nodes in the superconducting gap of hole-doped Ba 1Àx K x Fe 2 As 2 with x < 0:16 [14], in contrast to the nodeless gaps that have been found in electron-doped BaðFe 1Àx Co x Þ 2 As 2 [9]. It is hard to get a simple pairing mechanism from such complex situation of the superconducting gap structure.More intriguingly, nodal superconductivity has also been found in optimally doped BaFe 2 ðAs 0:67 P 0:33 Þ 2 (T c ¼ 30K) [15,16], in which the superconductivity is induced by isovalent P doping. Moreover, LaFePO (T c $6K) was found to display clear nodal behavior [17][18][19], and recently evidence for nodes in the superconducting gap of LiFeP (T c $ 4:5 K) has emerged from measurements of magnetic penetration depth [20]. The nodal superconductivity in these P-doped compounds is very striking, which raises the puzzling questions of whether, and why, the P doping is unique among iron-based superconductors. Although various theoretical explanations have been offered for this puzzle, investigators are far from reaching consensus [21][22][23][24][25].A recent empirical proposal is that the nodal state in ironpnictide superconductors, except for KFe 2 As 2 , is induced when the pnictogen height h Pn from the iron plane decreases below a threshold value of approximately 1:33 A [20]. According to this proposal, there may exist a transition from...

Background: Esophageal squamous cell carcinoma (ESCC) is a gastrointestinal malignancy with a poor prognosis. Although studies have shown metabolic reprogramming to be linked to ESCC development, no prognostic metabolic biomarkers or potential therapeutic metabolic targets have been identified. Method: The present study investigated some circulating metabolites associated with overall survival in 276 curatively resected ESCC patients using liquid chromatography/mass spectrometry metabolomics and Kaplan-Meier analysis. Tissue metabolomic analysis of 23-paired ESCC tissue samples was performed to discover metabolic dysregulation in ESCC cancerous tissue. A method consisting of support vector machine recursive feature elimination and LIMMA differential expression analysis was utilized to select promising feature genes within transcriptomic data from 179-paired ESCC tissue samples. Joint pathway analysis with genes and metabolites identified relevant metabolic pathways and targets for ESCC. Results: Four metabolites, kynurenine, 1-myristoyl-glycero-3-phosphocholine (LPC(14:0)sn-1), 2-piperidinone, and hippuric acid, were identified as prognostic factors in the preoperative plasma from ESCC patients. A risk score consisting of kynurenine and LPC(14:0)sn-1 significantly improved the prognostic performance of the tumor-node-metastasis staging system and was able to stratify risk for ESCC. Combined tissue metabolomic analysis and support vector machine recursive feature elimination gene selection revealed dysregulated kynurenine pathway as an important metabolic feature of ESCC, including accumulation of tryptophan, formylkynurenine, and kynurenine, as well as up-regulated indoleamine 2,3-dioxygenase 1 in ESCC cancerous tissue. Chen et al. Metabolic Features of ESCC Conclusions: This work identified for the first time four potential prognostic circulating metabolites. In addition, kynurenine pathway metabolism was shown to be up-regulated tryptophan-kynurenine metabolism in ESCC. Results not only provide a metabolite-based risk score system for prognosis, but also improve the understanding of the molecular basis of ESCC onset and progression, and as well as novel potential therapeutic targets for ESCC.