1. Département de Physique and RQMP, Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada


2. Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712, USA


3. Department of Advanced Materials, University of Tokyo, Kashiwa 277-8561, Japan


4. RIKEN (The Institute of Physical and Chemical Research), Wako 351-0198, Japan


5. RIKEN SPring8 Center, Hyogo 679-5148, Japan


6. Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada


7. These authors contributed equally to this work.


8. Present address: Ames Laboratory, Ames, Iowa 50011, USA.

Correspondence to: Louis Taillefer^1,6 Correspondence and requests for materials should be addressed to L.T. (Email: louis.taillefer@physique.usherbrooke.ca).

The Nernst effect in metals is highly sensitive to two kinds of phase transition: superconductivity and density-wave order¹. The large, positive Nernst signal observed in hole-doped high-T _c superconductors² above their transition temperature (T _c) has so far been attributed to fluctuating superconductivity³. 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 modulation⁴ that causes a reconstruction of the Fermi surface⁵. In La_2-xSr_xCuO₄ (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.