Enhancement of the Nernst effect by stripe order in a high-Tc superconductor

The Nernst effect in metals is highly sensitive to two kinds of phase transition: superconductivity and density-wave order(1). The large, positive Nernst signal observed in hole-doped high-T-c superconductors(2) above their transition temperature (T-c) has so far been attributed to fluctuating superconductivity(3). Here we report that in some of these materials the large Nernst signal is in fact the result of stripe order, a form of spin/charge modulation(4) that causes a reconstruction of the Fermi surface(5). In La2-xSrxCuO4 (LSCO) doped with Nd or Eu, the onset of stripe order causes the Nernst signal to change from being small and negative to being large and positive, as revealed either by lowering the hole concentration across the quantum critical point in Nd-doped LSCO (refs 6-8) or by lowering the temperature across the ordering temperature in Eu-doped LSCO (refs 9, 10). In the second case, two separate peaks are resolved, respectively associated with the onset of stripe order at high temperature and superconductivity near T-c.